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ELECTRICITY FOR 
EVERYBODY. 






f £^rul<rH~. 



ELECTRICITY EOR 
EVERYBODY; 

ITS NATURE AND USES EXPLAINED. 



BY 



PHILIP ATKINSON, A.M., Ph.D. 

AUTHOR OF "ELEMENTS OF STATIC ELECTRICITY," 

"THE ELEMENTS OF ELECTRIC LIGHTING," 

"THE ELEMENTS OF DYNAMIC ELECTRICITY AND MAGNETISM," 

"THE 'ELECTRIC TRANSFORMATION OF POWER." 



IReviseD anfc jSnlargefc 




NEW YORK 

THE CENTURY CO. 

1907 



' 



U8RARY of CONGRESS 
Two Copies Received 

JUN 3 i9or 

f7 Copyright JEnti 
1svUL 3,/ 



%K 



?0J 
LASS 6C XXc, No, 

COPY B. 



Copyright, 1895, 1897, 1907 
by The Century Co. 



THE DE VINNE PRESS 



INTRODUCTION. 

The*object of this book is to meet the public demand 
for information in regard to the nature and uses of 
electricity, and .the various kinds of apparatus by which 
it is generated v and employed. This information has 
been given in the simplest form consistent with clear- 
ness, fullness, and strict scientific accuracy, and with 
as little detail as possible; the constant aim of the 
writer being to make each topic so plain, that any per- 
son having no previous knowledge of electricity or 
kindred sciences, who gives the book a careful perusal, 
can obtain a good general knowledge of electric sci- 
ence in all its principal details ; the style throughout 
being adapted, as far as possible, to the requirements 
of the general reader rather than to those of the student. 

All mathematical demonstrations have been omitted, 
and all unnecessary technicality avoided; such techni- 
cal terms as are strictly required being fully explained. 
Only the latest and most approved apparatus and meth- 
ods have been described, matter of a merely historical 
character being omitted, or receiving only a passing 
notice. The principal electric units and instruments 
for electric measurement have been briefly described 
in connection with other matter, to avoid the wearisome 
detail of a full description in a separate chapter. 

Philip Atkinson. 

Chicago, May 6, 1895. 



\ 



PUBLISHERS' NOTE 
TO THE THIRD EDITION. 

The continued popularity of this book after the death 
of its author has led the publishers to prepare a new 
edition. This edition brings the work up to date and 
includes a chapter on " Wireless Telegraphy.' 7 

The work of revision has been done by a well-known 
expert who is a professor in one of the leading technical 
colleges. 



CONTENTS. 



CHAPTER I. 

Page 

The Nature of Electricity and Electric Transmission 1 

Nature of Electricity. — Energy. — Conservation of Energy. — 
Molecular Energy. — Ether. — Electric Transmission. — The 
Electric Current and Circuit. — Opening and Closing Electric 
Circuit. — Electric Induction. — Dielectrics. — Natural Electric 
Distribution. — Measurement of Electric Pressure and Current 
Volume. — Voltmeter. — Ammeter. — Electric Units. 



CHAPTER II. 

Static Electricity 20 

Elementary Principles. — Frictional Electric Generator. — The 
Leyden Jar. — Influence Machines. — The Atkinson Topler- 
Holtz Machine. — Spark Discharge. — Four-Plate Machine. — 
Static Induced Current. — Brush Discharge. — Report. — Direc- 
tion of Rotation. — The Wimshurst Machine. — Uses of Influence 
Machines. — Vacuum Tubes. — Lightning. — Return Stroke. — 
Thunder. — Lightning-Rods. — The Aurora. — Cause of the 
Aurora. 



CHAPTER III. 

Electric Batteries 57 

Elementary Principles. — Polarization. — The Smee Cell. — 
Zinc-Carbon Cells.— The Law Cell.— The Samson Cell.— The 
Leclanche Cells. — Potassium-Bichromate Cells. — The Grenet 
Cell. — Amalgamation of the Zinc. — The Edison-Lalande Cell. 
— Dry Cells.— Two-Fluid Cells.— The Daniell Cell.— Gravity 
Cells. — Bunsen and Grove Cells. — Battery Connections. — 
Comparison between Large and Small Cells. — Storage Bat- 



xii CONTENTS. 

teries.— The Plante Cell.— The Faure Cell.— The American 
Cell. — The Chloride Accumulator. — Electric Pressure and Rate 
of Discharge. — Electrolysis.— Electrolysis in Medical Practice. 
Electric Cautery. 

CHAPTER IV. 

Magnetism 93 

Elementary Principles. — Magnetic Lines of Force. — The 
Earth's Magnetism. — Agonic Line. — Steel Magnets. — Por- 
tative Force. — Effect of Breaking a Magnet. — Consequent 
Poles. — Magnetic Attraction and Repulsion. — Electromag- 
netism. — Deflection of the Magnetic Needle by the Electric 
Current. — Electromagnets. — Magnet Core. — Solenoids. — Am- 
pere's Theory of Magnetism. — Magnetism Generating Electri- 
city. — Induction Coils. — Electric Bells. 



CHAPTER V. 

Dynamos , 114 

Evolution of the Dynamo. — Direct Current Dynamos. — Series 
Wound Dynamo. — Shunt Wound Dynamo. — Compound Wound 
Dynamo. — Constant Current and Constant Potential. — Arma- 
ture Construction. — Construction of Brushes and Commutator. 

— Bipolar Dynamo. — Multipolar Dynamos. — Alternating Cur- 
rent Dynamos. — Transformers. " 

CHAPTER VI. 

Electric Motors 140 

Principles of Construction. — Counter Electric Pressure. — Re- 
lative Size of Dynamos and Motors. — Electric Distribution 
of Power. — Niagara Falls Electric Power Station.- 1 Loss of 
Power in Electric Transmission. — Stationary Motors. — Rheo- 
stats. — Reversal of Rotation. — Alternating Current Motors. — 
Two Phase Motors. — Single Phase Motors. — Railway Motors. 

— Electric Railways. — Running Cars by Storage Batteries. — 
Lightning Arresters. — Recording Watt-Meter. 



CHAPTER VII. 

Electric Lighting 165 

Heat and Light by Electric Resistance. — Arc Lighting. — 
Double Carbon Lamp. — Cut-Out. — Incandescent Lighting. — 
Parallel System of Electric Distribution. — Three-Wire System. 
— Alternating Current Distribution. — Tesla's Discoveries. 



CONTENTS. xlii 

CHAPTER VIII. 

Heat and Electricity 182 

Electric Heating. — Dewey Heater. — Carpenter Heater. — Ad- 
vantages of Electric Heating. — Electric Cooking. — Electric 
Ironing. — Electric Welding. — Electricity Generated by Heat. 

CHAPTER IX. 

The Telegraph and Telephone 193 

Simple Telegraph Equipment. — The Key. — The Sounder. — 
The Morse Alphabet. — The Relay. — Cut-Out and Lightning 
Arrester. — Repeaters. — Duplex Transmission. — The Neutral 
Relay. — Transmission by the Neutral Relay. — Condenser. — 
Transmitter. — The Polarized Relay. — Quadruplex Transmis- 
sion. — Automatic Transmission. — Submarine Transmission. 
Reflecting Galvanometer. — Siphon Recorder. — Automatic 
Transmitters. — Cable Alphabet. — Static Charge. — Operation 
of Condenser. — The Telautograph. — The Telephone. — The 
Bell Receiver. — The Blake Transmitter. — Difference between 
Telegraphic and Telephonic Transmission. — Construction of 
Telephone Circuit. — Cross Talk. — The Long Distance Tele- 
phone. — The Solid Back Transmitter. 

CHAPTER X. 

The Rontgen X-Rays 227 

Discovery of the Rays.— Generating Apparatus.— Compara- 
tive Permeability of Different Substances. — Fluorescence. — 
Fluorescent Screen.— The Fluoroscope.— Sciagraphs.— Na- 
ture of the Rays.— Practical Uses of the Rays.— X-Ray Illus- 
trations. 



CHAPTER XI. 

Wireless Telegraphy 253 

Invention of the Wireless Telegraph.— The Marconi Sending 
Apparatus.— The Coherer.— The Marconi Receiving Appar- 
atus. — Self-Restoring Detectors. — The Telephone as a Re- 
ceiving Instrument. — Interference Messages. — Tuned or a 
Syntonic Signalling.— Apparatus for Long Distance Trans- 
mission. Application of Wireless Telegraphy. 



ELECTRICITY FOR 
EVERYBODY. 



ELECTRICITY FOR 
EVERYBODY; 

ITS NATURE AND USES EXPLAINED. 

* 

CHAPTER I. 

The Natuee of Electeicity and Electeic 
Transmission. 

Nature of Electricity. — The prevailing- popular 
opinion that no one knows what electricity is, which has 
been current for so many years, is no longer strictly 
true. The laws of electricity are as fully and clearly 
understood now as those of heat, light, and gravity j and 
in its application to the various purposes for which it is 
employed, calculations based on these laws can be made 
with the greatest accuracy. 

Its nature is not so clearly understood as its laws, 
but this is equally true of heat, light, and gravity ; and 
by comparing it with these natural phenomena, and 
especially with heat, to which it seems to be closely 
allied, we obtain indications in regard to its nature on 
which a well-founded theory may be based, the truth of 
which can hardly be doubted. 

The theory prevalent forty years ago, that it is a fluid, 
or a combination of two fluids having opposite qualities, 



2 ELECTRICITY FOR EVERYBODY. 

like the oxygen and nitrogen of air, or the oxygen and 
hydrogen of water, has long since been abandoned, and 
no well-informed electrician ever speaks of it now as 
a fluid. 

Energy. — When, not many years ago, it was dis- 
covered that the principle which we call energy is a 
universal property of matter, a great search-light was 
turned on the dark places of science, revealing in beauti- 
ful simplicity what before was hidden and mysterious; 
and electricity especially received the benefits of this 
illumination. This principle, formerly recognized only 
in its most prominent, active forms, as in the living 
animal, the growing plant, the operating-machine, the 
glowing fire, the shining lamp, was found to exist also 
in bodies apparently destitute of it, as a stone, a brick, 
a log, a block of ice, or any other body ; energy being, 
in fact, inseparable from matter, and matter inseparable 
from energy. 

Conservation of Energy. — A second fact of equal 
importance is that energy, like matter, can neither be 
created nor destroyed. As it is impossible to create a 
single grain of sand out of nothing, or to reduce it to 
nothing, so it is equally impossible either to create or 
reduce to nothing a single particle of energy. But 
energy, like matter, can be changed from one form to 
another, or from one place to another. As ice can be 
transformed into water, and water into steam, or coal 
burned into ashes, cinder, soot, and gas, without a particle 
of loss, so energy can be transformed without loss: as 
when the energy of falling water or expanding steam is 
transformed into mechanical energy for the operation of 
machinery, — the total sum recovered as useful work and 
wasted in overcoming friction and inertia, or as heat, 



ELECTRICITY AND ELECTRIC TRANSMISSION. 3 

being* equal to the original quantity,- and the energy ex- 
pended at the water-wheel or the engine reappearing in 
its modified form in the mill or the factory. This trans- 
formation of energy, without increase or decrease, is 
what is known scientifically as the conservation of energy, 
the great fundamental doctrine of modern science, on 
which all the calculations of the civil or electric en- 
gineer, with reference to power, are based. 

Molecular Energy. — Energy manifests itself either 
in masses of matter, or in those infinitely small particles 
called molecules, of which the masses are composed. 
Hence we have the two kinds — mass energy and molecular 
energy. Mass energy becomes manifest in such familiar 
forms as gravity, as when a weight falls, or is attracted 
to the earth; magnetic attraction, as when a magnet 
attracts iron ; electric attraction, as when an electrified 
stick of hard-rubber or sealing-wax attracts bits of 
paper. Molecular energy becomes manifest by the move- 
ments of the molecules among themselves, of which we 
have familiar examples in the various kinds of chemical 
change by which new bodies are formed out of old ones, 
as soap out of alkali and grease, vinegar out of dilute 
alcohol. Heat is believed to be a certain mode of molec- 
ular motion, and the degree of intensity of this motion 
is expressed by the terms hot, cool, cold. In molten iron 
this motion has very high intensity, in ice very low in- 
tensity. Electricity is believed to be another mode of 
molecular motion, peculiar to itself, and different from 
that of heat. Just what that difference is, or what is the 
peculiar nature of the motion in each, has never been 
discovered. It is supposed to be in the form of undu- 
lations or vibrations, — the heat undulations having one 
form, the electric undulations another form : so that 



4 ELECTRICITY FOR EVERYBODY. 

while both kinds of motion are fonnd in the same body 
at the same time, they do not interfere with each other. 

When, therefore, the hand is placed on a hot body, 
that peculiar sensation which we feel, and call heat, is, 
according to this theory, simply the motion of the mole- 
cules ; and, in like manner, when the hand is placed on 
a body through which a very strong electric current is 
flowing, the peculiar sensation, different from that of 
heat, which is felt, is molecular motion in another form ; 
both produced by the same active principle which we call 
energy. And it is remarkable that the same effect is 
produced by contact with a body through which a suffi- 
ciently powerful electric current is flowing as by contact 
with a red-hot iron, — a burn being the result in each 
case, though the electrified body may be barely warm. 

If any one doubts the possibility of a vibratory motion 
of the molecules in such solid bodies as the metals, he 
should remember that bodies of apparently the greatest 
solidity are full of invisible pores, revealed only by the 
microscope, and of an infinitely greater number beyond 
the power of the microscope to reveal ; so that these in- 
finitesimal molecules, which far exceed the ability of the 
most powerful microscope to reveal separately, can move 
freely in these internal spaces. 

Ether. — These spaces, and the similar spaces in all 
other matter in the world and the universe, whether it be 
solid, liquid, or gaseous, are believed to be filled with a 
fluid called ether, which is so thin that it is impossible to 
perceive it, and which extends into the vast regions of 
space, where it is supposed that even the thinnest air 
does not exist ; and this ether is believed to be the 
medium by which electricity, and also light, is trans- 
mitted, and in part produced, by undulations, much in 



ELECTRICITY AND ELECTRIC TRANSMISSION. 5 

the same manner as sonnd is produced and transmitted 
by undulations of the grosser air, but with infinitely 
greater speed and facility, since ether is infinitely thinner 
than air, or any other gaseous fluid. There is a mutual 
reaction between the vibratory motion of the molecules 
and the undulatory motion of the ether, — the vibrations 
producing the undulations, and the undulations, in turn, 
producing the vibrations ; just as the vibratory strokes 
of the oar produce waves, which in turn produce vibra- 
tions in other oars resting in the water. 

The necessity for such a medium becomes apparent 
when we consider that energy cannot exist without mat- 
ter ; so that if these small internal spaces, and the great 
spaces between the heavenly bodies, were an absolute 
vacuum, the transmission of energy, in any form, would 
be an impossibility. Hence the existence of the ether is 
now universally accepted as a fact of which there can be 
no reasonable doubt, and which accounts in a rational 
manner for natural phenomena, especially those pertain- 
ing to light and electricity, which could not otherwise be 
satisfactorily explained. 

The conclusion, therefore, to which we come in regard 
to the nature of electricity is this: that electricity is a 
manifestation of energy, believed to consist in undula- 
tions of the ether, and vibrations of the grosser mole- 
cules of matter ; or, briefly, that it is a mode of molecular 
motion. 

We see, then, that it is neither energy nor matter, but, 
like heat, light, and sound, it is an effect produced by 
energy on matter. But as the effect cannot be separated 
from its cause, it is proper, and often convenient, to 
speak of it as electric energy, in the same sense as we 
speak of mechanical energy, vital energy, heat energy, or 



6 ELECTRICITY FOR EVERYBODY. 

energy in any other form in which it becomes manifest 
as associated with matter. 

Electric Transmission. — Electricity is transmitted 
through different substances with different degrees of 
facility. Those through which it can be transmitted 
easily, as most of the metals, especially silver, copper, and 
iron, are called conductors ; and those which resist its 
transmission so strongly that it will hardly pass through 
them at all, as hard-rubber, glass, and porcelain, are 
called non-conductors ; and the two opposite qualities thus 
shown are distinguished by the terms conductivity and 
resistance. Non-conductors, when employed to confine 
electricity, or prevent its transmission, are called insula- 
tors, and this confinement is expressed by the term insu- 
lation : as, for instance, copper wire is said to be insu- 
lated when enveloped in cotton, silk, gutta-percha, or 
any other non-conductor by which an electric current 
flowing through it is confined, and its transmission to 
another conductor prevented, by this insulation. 

It is not known why one substance permits the trans- 
mission of electricity, and another resists it ; but this is 
equally true of the transmission of heat and light, and 
may be ascribed, in each case, to some peculiar arrange- 
ment of the molecules ; so that transmission may result 
from harmony of molecular motion, and resistance from 
want of harmony: just as in the production and trans- 
mission of sound, the air-waves from one reed or string 
of an instrument may produce harmonic vibrations and 
a musical note in another reed or string occupy iug the 
proper relative position on the musical scale, or opposing 
waves may interfere and produce discord, or even silence. 
And it is very remarkable that the same substances show 
conductivity or resistance for electricity in about the 



ELECTRICITY AND ELECTRIC TRANSMISSION. 7 

same degree as for heat, — indicating clearly a close af- 
finity between the two, so that the same molecular ar- 
rangement affects each in about the same manner. 

The Electric Current and Circuit. — The trans- 
mission of electricity is produced by what is called elec- 
tromotive force, or electric pressure, which results from a 
greater accumulation of electric energy at one point than 
at another, producing a difference of the condition known 
as electric potential between them. The term positive 
expresses the condition of the point having the higher 
electric energy, and negative the relative condition of the 
other point ; terms used in the same sense as hot and cold 
in the similar relative conditions of heat potential. 

When two such points are connected by a conductor, 
electric energy flows from the positive point to the nega- 
tive — that is, from higher to lower potential, producing 
what is called the electric current. This would immedi- 
ately produce equality of potential between the points, 
and the flow would cease unless the difference of poten- 
tial were maintained, which can be done by an electric 
generator, either a battery or a dynamo, both of which 
will be described hereafter. 

This current, when employed for practical use, flows 
from the generator through a wire conductor to the place 
where it is used, and back through another wire to the 
generator 5 and this is what is known as the electric circuit. 
Either copper or iron wires are employed, according to 
the use for which the circuit is intended; or the earth 
may be made a part of the circuit, as in telegraph lines j 
or iron rails, as in electric railways. 

The current is impelled through the circuit by the elec- 
tric pressure at the generator, just as a current of steam 
is impelled through pipes by the generating pressure 



8 ELECTEICITY FOR EVERYBODY. 

at the steam-boiler, or of water by the hydrostatic 
pressure at the water-works. If electricity is a mode of 
molecular motion, as has been assumed, its transmission 
is simply the extension of this motion through the rows 
of molecules composing a wire or other conductor, by the 
vibrations and ether undulations, in much the same man- 
ner as vibrations are transmitted through a row of balls 
in contact, when produced by a blow at one end of the 
row, — the effect being seen in the bounding away of the 
ball at the opposite end ; the electric vibrations and un- 
dulations traveling with infinitely greater velocity than 
the grosser mechanical vibrations, so that they traverse 
one of the great ocean telegraph cables in a fraction of a 
second, or the distance between the sun and the earth in 
eight minutes. 

The volume of the current, with a given pressure, de- 
pends on the electric resistance of the circuit ; and this 
resistance depends on the kind of wire, or other material, 
of which the circuit, or any part of it, is composed, and 
the length and cross-section of this wire, or other con- 
ductor. A copper wire, for instance, has much less 
resistance than an iron wire of the same length and 
cross-section, and will therefore carry a current of propor- 
tionally greater volume with the same pressure. If the 
length of this wire is increased, or one of the same length 
but smaller cross-section substituted for it, the volume 
of the current will be proportionally reduced. But if the 
length is reduced, or a wire of the same length but larger 
cross-section substituted for it, the volume of the current 
will be proportionally increased. 

This resistance is very similar to the friction of- water, 
steam, or gas flowing through a pipe: the shorter the 
pipe, or the greater its cross-section, the less will be 



ELECTRICITY AND ELECTRIC TRANSMISSION. 9 

the friction and the greater the volume of current j and 
the longer the pipe, or the smaller its cross-section, the 
greater will be the friction and the less the volume of 
current. As the introduction of wool, cotton, or moss 
into such a pipe increases the friction, so the introduc- 
tion of a wire or other conductor of high electric re- 
sistance into the circuit at any point produces a similar 
effect. Thus a coil of German-silver or other wire of 
high resistance, a strip of composite metal, or a rod or 
fine strip of carbon, may be made a part of the circuit 
at any point, either to regulate the volume of the cur- 
rent, prevent increase of current volume beyond the 
safety limit, or produce electric light or heat. 

This whole matter of the relations of the electric cur- 
rent to electric pressure and resistance may be briefly 
summed up in the words of Ohm's celebrated law : The 
volume of an electric current varies directly as the electric 
pressure by which the current is impelled, and inversely as 
the total resistance encountered. 

Opening and Closing Electric Circuit. — The electric 
circuit is always arranged for the transmission or inter- 
ruption of the current by making an opening in it at any 




Fig. 1. 



convenient point, which may be closed for the transmis- 
sion of the current, or opened for its interruption, in 
various ways, as by a sivitch, or a spring operated by a 
push-button. The switch, in its simplest form, as shown 
in Fig. 1, is a strip of brass or copper which can be turned 



10 



ELECTRICITY FOE EVERYBODY. 




on a hinge by an insulating handle, and forms part of the 
circuit, which can thus be opened or closed. They are 
made in a great variety of forms adapted to various uses, 
some of them of very elaborate construction, but all on 

the same general 
principle. The 
push-button, 
shown in Fig. 2, 
is well known in 
connection with 
the electric bell : 
a brass spring 
which forms part 
of the circuit 
Fi g- 2 - closing the open- 

ing when pressed by an insulating button of hard-rubber, 
porcelain, or fiber, — the whole inclosed in a cap made in a 
great variety of ornamental designs. 

When a circuit is arranged to be kept closed constantly 
by a switch when in use, as in electric lighting and many 
other kinds of electric work, it is known as a closed circuit; 
but when arranged to remain open most of the time, and 
be closed and opened alternately in rapid succession when 
in use, as in the ringing of electric bells, it is known as an 
open circuit. 

Electric Induction.— There is a certain kind of elec- 
tric transmission which has received the name of induc- 
tion, which occurs between an electrified body and other 
bodies in its vicinity, from which it is insulated. This 
body may be a conductor through which a current of 
electricity is flowing, or a body electrified in some other 
way, as by a charge from a glass-plate electric machine, 
or by friction, as when a rod of hard-rubber or a stick of 



ELECTRICITY AND ELECTRIC TRANSMISSION. 11 

sealing-wax is rubbed, or by a natural charge, as that 
acquired by a thunder-cloud. 

Induction can occur only when the electrified body is 
insulated, otherwise the transmission would be through 
a conductor, as already described : so that it is impossible 
to insulate against it, as this influence traverses not only 
the insulating substance by which the electrified body is 
immediately surrounded, but all other bodies within its 
range, whether conductors or non-conductors, — the resis- 
tance which it encounters in different bodies being in 
similar proportion to the resistance encountered in other 
transmission, though far less in degree. 

Another very remarkable peculiarity of induction is 
this : that it produces in conductors which come within 
its influence an electric potential opposite to that in the 
body from which it proceeds, — positive potential in the 
one producing negative potential in the other, and neg- 
ative producing positive. A positively electrified cloud, 
for instance, floating in the insulating air, produces neg- 
ative potential in the earth beneath it; and a negatively 
electrified cloud, positive potential in the earth : so that 
a lightning-stroke would, in the first instance, be from 
the cloud to the earth, and, in the second, from the earth 
to the cloud. 

From this we must infer that the electricity, in passing 
through the insulating medium by which it is immediately 
surrounded, undergoes a change, so that it repels elec- 
tricity from surrounding bodies, when the potential of 
the electrified body is positive, or attracts it when nega- 
tive, as exemplified in the case of the cloud and the earth ; 
the tendency being to so balance the positive and negative 
between the electrified body and the bodies within its 
inductive influence, by making the positive potential of 



12 ELECTRICITY FOR EVERYBODY. 

the one equal to the negative potential of the other, that 
electric transmission between them, through a conductor, 
would produce perfect equilibrium. 

This electric influence, traversing both conductors and 
non-conductors, is strong proof of the existence of a me- 
dium which permeates both, and indicates that the ether, 
already described, is that medium. 

Dielectrics. — It should be remarked that non-conduc- 
tors, or insulators, when referred to in connection with 
induction, are called dielectrics, a word intended to signify 
that electricity can pass through them in the manner de- 
scribed. 

A curious effect of induction, which has a most impor- 
tant practical bearing, is that when wires traversed by 
electric currents are placed in each other's vicinity, as in 
telegraph and telephone lines, the inductive effect of each 
current is to reduce the strength of the current in any 
adjacent wire, when both currents flow in the same direc- 
tion, or to increase it when they flow in opposite direc- 
tions. The reason of this is that the flow of an electric 
current is always from positive potential to negative, so 
that the positive potential of each wire creates a limited 
degree of negative potential in the adjacent end of the 
other wire, and the negative potential at the opposite end 
of each creates a limited degree of positive potential in 
the adjacent end of the other ; and this condition tends to 
produce a current flow in each in the opposite direction 
to that of the current which induces it, by which the 
strength of the original current is reduced when it flows 
in the same direction as the inducing current, but in- 
creased when it flows in the opposite direction. - 

The inductive influence is radiated equally in all direc- 
tions from the electrified body, just as light is radiated 



ELECTRICITY AND ELECTRIC TRANSMISSION. 13 

from a lamp, or heat from a stove ; so that each body 
coming within this influence receives only so much of 
the limited quantity of electricity radiated as is contained 
in the rays which it intercepts. A body one foot distant 
receives four times as much as one two feet distant, be- 
cause it intercepts four times as many of the diverging 
rays j or nine times as much as one three feet distant, be- 
cause it intercepts nine times as many rays : from which 
we derive the law that induction varies inversely as the 
square of the distance — that is, the greater the distance, 
multiplied into itself, or squared, the less proportionally 
is the induction. Hence it will be seen that a wire will' 
receive only a very small part of the inductive influence 
radiated equally all around from an adjacent wire one 
or two feet distant. 

Natural Electric Distribution. — When we speak of 
electrified bodies, the expression should be understood in 
the same relative sense as we speak of heated bodies, 
meaning thereby bodies whose temperature has been 
raised above the average temperature we are accustomed 
to find in such bodies. But as all bodies possess a certain 
natural quantity of heat in different degrees under varied 
conditions, so all bodies possess a certain natural quantity 
of electricity in different degrees under varied conditions 5 
and we have an atmosphere of high or of low electric 
potential, just as we have an atmosphere of high or of 
low heat potential — that is, a hot or a cold atmosphere. 
And we find natural electric currents both in the earth 
and atmosphere, and areas of high or low electric poten- 
tial, just as we find similar natural warm or cold areas, or 
currents of warm or cold air or water. 

Familiar examples of such areas of high electric poten- 
tial are seen in the aurora, and of electric currents in the 



14 ELECTRICITY FOR EVERYBODY. 

shooting rays which emanate from the auroral arch, and 
the earth currents which always accompany the auroral 
display and produce disturbance in telegraph lines. And, 
in the thunder-cloud and the inductively electrified earth 
beneath it, we have a familiar example of more limited 
electrified areas ; and, in the vivid chain-lightning, of a 
transient electric current. 

In the electric equilibrium which ordinarily prevails in 
all bodies by which we are surrounded, the presence of 
electricity is not perceived, just as, under similar condi- 
tions, the force of gravity is not perceived ; and it is only 
when these conditions are disturbed, either by natural 
means, as in the aurora and the thunder-cloud, or by 
artificial, as in the battery and the dynamo, and a differ- 
ence of electric potential produced, that we become 
conscious of the presence of electricity j just as we be- 
come conscious of the force of gravity in the falling 
weight, when a difference of gravity potential has been 
produced. 

It cannot reasonably be doubted that this all-pervading 
force is an important element in the animal economy, 
and that our health and vigor, our physical and mental 
states, are largely dependent on electric conditions, in- 
ternal and external. Intelligent physicians have come to 
recognize its importance in the treatment of disease, and 
to employ it as a valuable remedy. And as its physio- 
logical relations come to be more fully understood, its 
value as a remedial agent will doubtless be more fully 
appreciated. 

Its influence in the vegetable economy is doubtless as 
great as in the animal, and the life and vigor of the 
growing plant are probably largely due to this influence ; 
so that the field for electric experimental research may 



ELECTRICITY AND ELECTRIC TRANSMISSION. 



15 



yet be found full of important revelations both to the 
botanist and the physician. 

Measurement of Electric Pressure and Current 
Volume. — Electric pressure is measured by a meter, just 
as steam pressure is measured by a gauge ; and current 
volume is measured by a similar meter differently applied. 
One of the most common instruments for the former pur- 
pose is shown in Fig. 3, and its internal construction in 
Fig. 4. 

Yolt-meter. — A brass case, shown in Fig. 3, incloses a 
steel magnet of the same shape as the outside of the case, 
its two poles termi- 
nating in the nar- 
row space in front, 
as shown in Fig. 4. 
These poles produce 
what is called a mag- 
netic field within this 
space — that is, a 
space permeated by 
a strong magnetic 
influence; lines of 
magnetic energy, 
which is similar to electric energy, traversing it con- 
tinually from pole to pole. 

In order to make this field as strong as possible, and 
to distribute this influence just where it is wanted, two 
soft iron pole-pieces are attached to the poles, as shown, 
which inclose a circular space in which is mounted, in a 
fixed vertical position, a soft iron cylinder. The mag- 
netic lines traverse the iron pole-pieces and cylinder 
much more easily than they would traverse a similar 
space filled with air, and produce strong magnetic in- 




Fig. 3. 



16 



ELECTRICITY FOR EVERYBODY. 



duction, which is similar to electric induction, in the 
narrow air-space between the cylinder and pole-pieces. 
Within this space a coil of fine insulated copper wire, 
wound on a light copper frame, is mounted, as shown, 




Fig. 4. 

and has a limited rotary motion in opposition to the 
force of the two oppositely coiled flat spiral springs 
shown above and below, by which a light aluminum 
pointer, shown at the left above, is moved to the right 
over the graduated scale shown in Fig. 3. 

This coil is connected, through the two springs, with 
the electric circuit at any point where it is desired to 
measure the electric pressure,— the connection being made 
by the binding-posts shown on opposite sides in Fig. 3; 
the instrument beiug always placed between the two 



ELECTRICITY AND ELECTRIC TRANSMISSION. 17 

wires of the electric circuit, so that the current, or rather 
a very small fraction of it, must flow through the coil, 
across from the positive to the negative wire, and thus 
show the difference of potential which produces the elec- 
tric pressure at that point. 

When the circuit is closed for a moment by a contact 
key, and the current flows in this way, the coil tends 
to rotate into a position in which the current shall cross 
the greatest number of lines of magnetic force flowing 
from pole to pole ; and this rotation being always in 
exact proportion to the electric pressure, in opposition to 
the force of the springs, is indicated on the scale shown 
in Fig. 3, in degrees, each of which represents the electric 
pressure unit known as the volt. Hence this instrument 
is called a volt-meter. 

There are two scales shown, the outer one indicating 
volts, and the inner one twentieths of a volt, by degrees 
of corresponding width ; and the current flows through a 
coil of wire of high resistance, not shown, which is made 
a part of the circuit through connections with each of 
the two binding-posts shown on the left, — this coil being 
tapped at different points, so as to include a long section 
and hence high resistance, for strong pressure, indicated 
in volts on the outer scale, when connection is made with 
the front binding-post; or a shorter section, and hence 
lower resistance, for weaker pressure, indicated in twenti- 
eths of a volt on the inner scale, when connection is made 
with the rear binding-post. 

Back of the right binding-post is shown the contact 
key referred to above, by which the circuit can be closed 
when the instrument is in use. There is also a coil con- 
nected with this key, by which the instrument can be 
regulated, or calibrated, as this regulation is called. 



18 



ELECTRICITY FOR EVERYBODY. 




Fig. 5. 



Ammeter. — In Fig. 5 is shown an instrument of simi- 
lar construction, but much simpler, by which the volume 
of the electric current is measured. This instrument has 
no resistance coil, and only one scale, and hence requires 

only the two bind- 
ing-posts shown on 
the right. Its cop- 
per coil is of coarser 
wire, and therefore 
carries a current of 
greater volume; and 
the instrument is 
not connected with 
opposite circuit- 
wires, like the volt- 
meter, but directly 
in the circuit, so that the whole current can flow through 
it, and therefore it shows current volume and not elec- 
tric pressure. This is indicated in degrees on the scale, 
each of which represents the electric current uuit known 
as the ampere. Hence this instrument is called an am- 
pere-meter, or, briefly, an ammeter. The ammeter is often 
permanently connected with the electric circuit, but the 
volt-meter is usually connected only while making tests 
to ascertain the electric pressure. But volt- meters of 
special construction, known as potential indicators, are 
permanently connected. 

Electric Units. — Electric units are as necessary in 
electric measurement as units of weight, money, length, 
or area, in our ordinary transactions ; and, like the pound, 
the foot, the dollar, are the standards to which, we con- 
stantly refer, and by which we form comparative esti- 
mates, and make electric calculations. The three princi- 



ELECTRICITY AND ELECTRIC TRANSMISSION. 19 

pal electric units, and the only ones necessary to define 
at present, are the volt, the unit of electric pressure, the 
ohm, the unit of electric resistance, aud the ampere, the 
unit of electric current strength. 

The volt represents an electric pressure nearly equal to 
that of a Daniell battery cell, described in Chapter III. 

The ohm represents the electric resistance which 
would be encountered by an electric current flowing 
through a column of pure mercury, at the temperature of 
0° Centigrade, 106 centimeters in length, and 1 square 
millimeter in cross-section ; or, to make this more in- 
telligible to the ordinary reader, such a column, at the 
temperature of 32° Fahrenheit (or freezing-point), 41 3^ 
inches in length, and about ^^o o of a square inch in 
cross-section. This would resemble the column of mer- 
cury in an ordinary thermometer, increased to 41^^ 
inches in length. 

The ampere represents the volume of a current pro- 
duced by a pressure of 1 volt flowing through a con- 
ductor having a resistance of 1 ohm. 



CHAPTER II. 

Static Electricity. 

Elementary Principles. — Static electricity does not 
differ in its nature from electricity in any other form ; 
but is called static because it does not usually now con- 
tinuously in currents, as electricity in other forms, but is 
accumulated in condensers, from which it is discharged 
instantaneously; a striking example of which we have 
in the thunder-cloud. In this respect it may be com- 
pared to water accumulated in a lake or reservoir, while 
current electricity may be compared to water in a run- 
ning stream. 

It was under this form that electricity was first dis- 
covered, and for more than two thousand years remained 
undeveloped, without attracting any attention, except as 
a curious property supposed to belong to only one or 
two substances, and having no practical value whatever. 
Its first discovery was in connection with amber, which 
when rubbed was found to have the power of attracting 
light bodies. Hence this property was called electricity, 
a name derived from electron, the Greek name for amber. 
It was subsequently discovered that this property could 
be developed by friction in jet also ; and about the year 
1600 it was found by Gilbert, an English scientist, in a 
large number of substances, prominent among which 
were sulphur, glass, and sealing-wax. 

It was also found that while bodies electrified in this 

20 



STATIC ELECTRICITY. 21 

way attracted un electrified bodies, they repelled them af- 
ter a moment's contact, or as soon as the attracted body 
acquired the same electric potential as the attracting.body. 
This curious effect was extremely puzzling to scientists, 
and gave rise to different theories as to the nature of elec- 
tricity to account for it. But the simple fact, fully veri- 
fied by observation, that repulsion results from equality 
of electric potential between bodies^ and attraction from 
difference of electric potential between them, accounts for 
both phenomena in a perfectly rational and satisfactory 
manner. 

About the year 1750, Otto von Guericke, a German 
scientist, conceived the idea of generating electricity by 
the friction of the hands on a rotating globe of sulphur; 
and this was the first electric machine. Newton substi- 
tuted a glass globe for the sulphur globe; and various 
other improvements followed, a glass cylinder being sub- 
stituted for the globe, and afterward a glass plate for the 
cylinder, — the friction being produced by a pair of leather 
cushions instead of the hands. A condenser for collect- 
ing the electricity was also added, which at first was 
simply an insulated iron tube, for which an insulated 
cylinder or globe of brass was afterward substituted. 

Frictional Electric Generator. — The frictional 
electric machine thus gradually developed is shown in 
its latest improved form in Fig. 6, and is constructed 
with a circular glass plate mounted on insulating wooden 
or glass posts, and having a crank by which it can be 
rotated. On the right of this plate is a pair of rubbers, 
made of leather-faced cushions smeared with an amalgam 
of tin, lead, and mercury, made into a paste with lard. 
These are pressed against the plate by a pair of brass 
springs having a bolt and screw to adjust the pressure, 



22 



ELECTRICITY FOR EVERYBODY. 



and are attached to an insulating glass post surmounted 
by a brass ball. On the left is a brass globe employed 
as a condenser, and known as the prime conductor, which 
is insulated on a glass post ; and from a brass ball below 




Fig. 6. 

it a pair of brass combs, with sharp points for collecting 
the electricity, project to the right on opposite sides of 
the plate ; a brass rod terminating in a ball projecting in 
the opposite direction, for convenience in connecting ap- 
paratus with the machine. 

When the plate is rotated by the crank in the direction 
indicated by the arrow, a difference of electric potential 
between it and the rubbers and parts connected with them 
is produced by the friction ; electric energy being trans- 
ferred from the one to the other, so that the one becomes 
positive to exactly the same degree as the other becomes 
negative. 

It is generally assumed that this transfer of energy is 
from the rubbers and connected parts to the plate, mak- 



STATIC ELECTRICITY. 23 

ing the plate positive and the rubbers negative ; the sup- 
ply of electric energy being obtained from the earth 
through the conducting chain shown on the right. But 
if the transfer is in the opposite direction, as may be the 
case, making the plate negative and the rubbers positive, 
then electric energy must pass to the earth through the 
chain. 

The lower half of the plate is enveloped in an insulat- 
ing silk bag, by which the electric charge, whether posi- 
tive or negative, is confined to its surface; and when this 
charged surface comes round to the combs, the charge is 
transferred by them to the prime conductor; electric 
energy passing from this surface, if positive, or to it, if 
negative, — the charge thus acquired by the prime con- 
ductor being just as strong in the one case as in the 
other. By transferring the chain to the prime conductor, 
the relative electric potential of it and the rubbers is 
reversed. 

Pointed combs are employed to collect the electricity, 
because a point, having no surface, has no electric resis- 
tance ; so that electricity flows freely either to it or from 
it. But globes and balls are employed in this machine 
and elsewhere to confine the electricity by their surface 
resistance, because a globe, having neither angles nor 
edges, has the highest surface resistance, and electricity 
in the static form always collects on the surface of charged 
conductors, and in the current form tends to the surface, 
being repelled from the interior by the equality of poten- 
tial in the charged body, and attracted outward by the 
difference of potential between this body and surround- 
ing bodies, in accordance with the principle already given; 
so that its tendency is to escape through the air to sur- 
rounding bodies, — points, angles, and edges facilitating 



24 



ELECTRICITY FOR EVERYBODY. 



this escape. Hence they should be avoided in the con- 
struction of electric generators and other electric appa- 
ratus, except where strictly required. 

The quantity of electricity generated by this machine 
is comparatively small, and hence the machine is not 
adapted to any practical use, and is employed only to 
illustrate the principles of electricity ; and even for this 
purpose it is now but little used, having been superseded 
by generators of static electricity of much higher electric 
efficiency ; so that it has now little more than a historic 
value. 

The Leyden Jar. — Before describing these improved 
generators, it is important that the apparatus known as 
the Leyden jar should be described. This apparatus, which 
derives its name from the place of its discovery, is shown 
in Fig. 7, and consists of a glass jar coated inside and 

outside with tinfoil, or 
some other thin sheet- 
metal, except three or 
four inches at top, left 
uncoated for insula- 
tion between the coated 
surfaces. This jar is 
closed with an insu- 
lating cover, through 
which a brass rod ex- 
tends to the inside coat- 
ing, and terminates 
above in a ball. 
When a charge of electricity is given to the inside coat- 
ing through this rod, by an electric machine, the outside 
coating becomes oppositely charged by induction, when 
connected with the earth or with the oppositely charged 
part of the machine. 




Fig. 7. 



STATIC ELECTRICITY. 



25 



In this way a charge of very high electric energy may 
be accumulated, varying in proportion to the area of 
coated surface. This surface may be produced in a single 
jar, or in a number of jars connected together as a Ley den 




Fig. 8. 

lattery, as shown in Fig. 8, by connecting together all 
their inside coatings by conductors attached to the rods, 
and likewise all their outside coatings in any convenient 
manner, as by a sheet of tinfoil, — the two surfaces thus 
becoming practically the same as those of a single jar 
having the same area of coated surface. 

The glass in such a jar must be of the best insulating 
quality, either green glass or flint, having no lead or other 
conducting substance in its composition. It is not es- 
sential that it should be in the form of a jar, except for 
convenience in use; a glass plate or cylinder coated in 



26 ELECTRICITY FOR EVERYBODY. 

the same way being capable of receiving a similar charge. 
It is also immaterial whether the coating is cemented to 
the surface, as is necessary with a flexible coating like 
tinfoil, or is merely kept in contact with it, as may be 
done with a rigid coating like sheet brass. 

When a connection is made between the inner and 
outer coatings of a charged jar or battery, as may be 
done with a curved brass rod with an insulating handle, 
called a discharger, as shown in Fig. 7, there occurs an 
instantaneous transfer of electric energy from the coat- 
ing positively charged to the one negatively charged, 
accompanied with a bright spark and a loud report, as 
this energy rushes through the resisting air between the 
knob of the jar and the knob of the discharger. The 
transfer is from the inside coating, if positively charged, 
or to it, if negatively ; equality of potential between the 
coatings being thus restored, except a small residual 
charge which remains in the glass, and may be dis- 
charged in a similar manner after a few moments of 
rest, — several such residuals, of constantly decreasing 
energy, being often obtained in succession. This proves 
that the charge produces an electric strain in the insu- 
lating glass, requiring time for the glass to resume fully 
its original condition. 

If the glass is thin at any point, it may not have suffi- 
cient strength to resist this strain when the jar is heavily 
charged, and a discharge producing a small perforation, 
in which the glass becomes pulverized, surrounded by a 
star-like fracture, is liable to occur, which destroys the jar 
for future use. A spontaneous discharge without per- 
foration is also liable to occur over the uncoated surface, 
in case of an overcharge. 

A jar may retain its charge for several hours in a dry 



STATIC ELECTRICITY. 27 

atmosphere, being meantime slowly discharged through 
the air. But it is quite impossible for either surface to be 
discharged, either instantly through a discharger, or slowly 
through the air, without producing an equal change of 
potential on the opposite surface, electricity always pass- 
ing from the positive surface to the negative. Hence 
the charge on either surface, whether positive or negative, 
is said to be bound by the opposite charge. 

The discharge from a small jar, no larger than a half 
pint, passed through the body, will produce a very severe 
shock j and a sufficient charge can be accumulated in a 
large battery, or a single jar having an equal area of 
coated surface, to kill a man ; instances being on record 
of eminent scientists who were killed or injured in this 
way. But a full charge from a large battery may be 
passed harmlessly through the body if received through 
the point of a fine sewing-needle held in the hand ; the 
discharge, in such case, being gradual and silent, iu stead 
of instantaneous, with spark and report, as when passed 
through the ball-tipped discharger, — forcibly illustrating 
the difference of electric resistance between a point and a 
globe or ball, as already explained. 

Influence Machines. — In 1865 Dr. Holtz, a German 
scientist, invented a machine in which electricity was 
generated by the inductive influence of two glass plates 
on each other, after a small initial charge, generated by 
friction on a piece of hard-rubber, was given to one of 
them. This machine was a far more powerful generator 
than the frictional machine, as it could accumulate a much 
greater charge; and was constructed with a great deal of 
care, its construction including many important features 
which have since been extensively copied, producing a 
class of similar generators known as influence machines. 



28 ELECTRICITY FOR EVERYBODY. 

The principal defect in the Holtz machine was its lack 
of constancy and reliability as a generator nnder unfa- 
vorable atmospheric conditions, the initial charge being 
rapidly dissipated in a damp atmosphere, so that the 
machine would either entirely fail to generate, or would 
cease while in operation by a sudden change of atmo- 
spheric conditions. 

The Atkinson Topler-Holtz Machine. — To remedy 
this defect, Topler, another German scientist, constructed, 
about the same time, a similar machine in which the 
initial charge was constantly sustained by frictional ap- 
paratus connected with the machine itself , making it self- 
exciting. This machine, to which some minor improve- 
ments were added by a mechanic named Voss, was further 
improved by the writer, to whom United States patents 
protecting these improvements were granted in 1883 and 
1885. Its construction will be easily understood from 
Fig. 9. 

Two glass plates, A and B, well coated with shellac, are 
mounted vertically on a wooden stand, within about a 
quarter of an inch of each other. B, whose diameter is 
about two or three inches greater than that of A, is sup- 
ported on insulators in a fixed position, and known as the 
stationary plate ; and A is attached to a central insulating 
hub, supported on a spindle which passes through a large 
hole in the center of B, and is attached to a post in the rear 5 
so that this plate can be rotated by a driving wheel and 
belt, as shown, and is therefore called the revolving plate. 

Both these plates are made of the best insulating sheet 
glass, and being on independent insulating supports, are 
entirely insulated from each other. All the insulators 
are made of hard-rubber, and the base and post of kiln- 
dried wood, which is also an insulator of medium quality. 



STATIC ELECTEICITY. 



29 



On the rear of plate B are cemented two paper inductors 
X and T, under each of which is cemented a pair of tin- 
foil disks connected by a tinfoil strip, and each pair con- 
nected separately, by similar strips, with the brass wire 




Fig. 9. 

brushes U and F. And on the front of plate A are ce- 
mented six disks of sheet brass, called carriers, having 
raised centers which make contact with the brushes when 
the plate revolves, generating the initial charge. 

Two brass combs, K and L, are supported opposite the 
inductors, in a horizontal position, by insulating rods at- 
tached to a central insulating disk M, and are connected 
by brass rods with the inside coating of two Ley den jars 



30 ELECTRICITY FOR EVERYBODY. 

C and D. And attached to the same disk, at an angle of 
45 degrees with the horizontal combs, are two brass 
combs V and 27, electrically connected with each other, 
through the disk M, by attachment to a brass center ; and 
to each of these is attached a brass wire brush, which, 
like the other pair of brushes, makes contact with the 
carriers. 

Attached to the knobs above the jars are two brass 
sliding-rods P and R, having insulating handles. These 
rods can be brought into contact or separated to any re- 
quired extent, and are employed as dischargers. 

The outer coatings of the jars are made of sheet brass, 
and connected, under the base, by copper wires, to the 
switch 8, through which, when closed, an electric dis- 
charge can pass between the coatings, or by opening 
which it can be diverted through connecting sockets and 
flexible conducting-cords so as to pass through a person 
holding the terminal handles, or through any piece of 
apparatus connected with the terminals' of these cords. 

When the switch is closed, the sliding-rods separated, 
and the plate A rotated in the direction indicated by the 
arrows, a small initial charge is generated by the friction 
of the brushes on the carriers, electric energy being 
transferred either from the carriers to the inductors, or 
oppositely, during their momentary connection through 
the brushes. If inductor X, for instance, receives electric 
energy from carrier Z, then the potential of X becomes 
positive, and that of Z relatively negative, while these 
conditions are reversed between inductor Tand carrier 
Wb/ the friction produced at the same instant; T becom- 
ing negative, and W relatively positive, by the transfer 
of energy in the opposite direction. 

As Z with its negative charge moves up past the comb 



STATIC ELECTRICITY. 31 

K, electric energy flows to it, through this comb, from the 
inside coating of jar C ; and as TT, at the same instant, 
moves down with its positive charge past the comb X, 
electric energy flows from it, through this comb, to the 
inside coating of jar D. Hence the inside coating of C 
becomes negative and that of _D positive, and their out- 
side coatings become oppositely charged by induction j 
electric energy being repelled from the outer coating of 
D, through the switch and its connections, to the outer 
coating of G, making that of D negative and that of C 
positive. 

But each of these carriers has a residual charge left in 
it, after passing the insulated comb, which is increased 
by the influence of the inductor opposite which it passes 5 
so that Z arrives at comb and brush V with a negative 
charge, and W at comb and brush H with an equal pos- 
itive charge. But as combs V and H are connected 
together by conductors, there is an instant transfer of 
electric energy from W to Z 1 through these connected 
combs, and equality of potential is almost completely 
restored between them ; so that W comes round to brush 
F and Z to brush E with only a very slight residual, and 
the previous process is again repeated. 

Now as there are six carriers, each of which goes 
through this process at each full revolution of the plate, 
becoming alternately negative and positive at each half 
revolution, and contributing its quota to the opposite 
charges accumulating on the inductors and opposite 
coatings of the two jars, it is evident that at the end of 
the first revolution the initial charge will be six timts as 
great as at first, and the inductive influence of the in- 
ductors and carriers on each other, which has meantime 
been accumulating in geometrical ratio, will be many 



32 ELECTRICITY FOR EVERYBODY. 

thousand times as great. And as the plate makes about 
five revolutions per second, at ordinary speed, the rate of 
increase of the inductive charge by continual multiplica- 
tion into itself becomes enormously great, even at the 
end of the first second ; so that the initial charge, at first 
imperceptible, spreads from the tinfoil to the paper in- 
ductors, and thence over the surface of the stationary 
plate; and, in like manner, from the carriers over the 
surface of the revolving plate, till the electric pressure, 
amounting to many thousand volts, equals the resistance 
of the insulating parts of the machine and the surround- 
ing air, — opposite surfaces, and opposite halves of the 
same surface, in both plates, becoming oppositely charged. 
The charge spreads over the insulating surfaces with a 
crackling noise, and, in the dark, brushes of light may 
be seen streaming from or to the combs. 

Spark Discharge. — When a sufficient charge has ac- 
cumulated to overcome the electric resistance of the air 
between the sliding-rods, a discharge occurs, accompanied 
with a spark and report; electric energy being trans- 
ferred from the positively charged inner coating of one 
jar to the negatively charged iuner coating of the other, 
with corresponding restoration of equality of electric po- 
tential in all parts of the machine. If the transfer of 
electric energy during the accumulation of the charge 
is in the direction which has been assumed, as it usu- 
ally is, then the discharge will be from the inside coating 
of D to that of C— that is, from E to P. But if the trans- 
fer is in the opposite direction, as frequently happens, 
then the discharge will be from P to R. 

The reason why there should be a transfer. of electric 
energy in any given direction rather than in the opposite 
direction during the accumulation of the charge, is not 



STATIC ELECTRICITY. 33 

entirely clear, but is partly accounted for by a difference 
of insulation of the parts. The upper parts of the plates, 
where brush E is attached, being better insulated than 
the lower parts, where brush F is attached, by their 
greater distance from the base and adjacent objects, is 
probably the reason why jar D usually acquires a higher 
charge than jar 0, and a positive charge on its inside 
coating; the rotation of the upper part of plate A being 
toward jar D, and that of its lower part toward jar C, 
each jar receiving its charge from that part which ro- 
tates toward it. 

The length of the spark, as measured by the distance 
between the knobs of the sliding-rods, which also mea- 
sures the resistance of the air, varies as the electric 
pressure of the charge. By increasing this distance in 
proportion to the pressure, the highest pressure obtain- 
able from a machine may be ascertained. This, as indi- 
cated by the spark, varies as the diameter of the plates 
and the insulating quality of the glass ; the spark length 
ranging from 4J inches in machines with plates 14 and 
16 inches in diameter, to 1\ inches in machines with 
plates 25 and 28 inches in diameter. 

The frequency of the spark, at a given rate of speed, 
must be taken in connection with its length as an indi- 
cation of the full electric efficiency ; and this varies as 
the number of plates of a given size in the machine and 
the area of coated surface in the Ley den jars. 

Four-Plate Machine. — Machines of this kind may be 
constructed with as many pairs of plates, combs, and 
brushes as can be conveniently combined together j four- 
plate machines being common, in which the relative po- 
sitions of each pair of plates are reversed, as shown in 
the sectional view of such a machine in Fig. 10; the 



34 



ELECTRICITY FOR EVERYBODY. 



two stationary plates, with their rear surfaces turned 
toward each other, being placed between the two re- 
volving plates, which have their carrier-bearing surfaces 

turned to the front and 
rear. This is, in fact, a 
double machine, with a sin- 
gle pair of Ley den jars and 
discharging-rods. Eight- 
plate machines may be con- 
structed by a similar com- 
bination of two four-plate 
machines j but no increase 
of electric efficiency can be 
obtained by the mere mul- 
tiplication of plates with- 
out a corresponding multi- 
plication of combs, brushes, 
carriers, and inductors. 

The frequency of the 
spark, with a given number 
of plates, varies as the area of coated surface in the Leyden 
jars : the smaller this area, the more frequent the spark, 
and the less proportionally is its energy ; and the larger 
this area, the less frequent the spark, and the greater pro- 
portionally is its energy. 

Electric pressure is not dependent on the number of 
plates, but on their diameter; being no greater in a four- 
plate or an eight-plate machine than in a two-plate having 
plates of the same diameter. 

Length and frequency of spark are only rough indica- 
tions of electric efficiency. No instrument has yet been 
invented for accurate measurement of the full electric 
efficiency of these machines; but approximately accurate 




Fig. 10. 



STATIC ELECTRICITY. 35 

measurement of their electric pressure may be ascer- 
tained by an instrument known as the electrometer. 

Static Induced Current. — When a discharge occurs 
between the inner coatings of the jars through the slid- 
ing-rods, there is an equal discharge in the opposite di- 
rection, between the outer coatings, through the switch 
and its connections, which may be shown by a spark be- 
low, between the switch terminals, simultaneous with the 
spark above, when the switch is open so as to leave an 
air-space of half an inch or less between its terminals. 
This discharge may be changed to an intermittent, pul- 
sating current, by having the sliding-rods separated very 
slightly and the switch open to the same limited degree, 
producing a succession of very rapid discharges, which 
gives the lower spark the appearance of being contin- 
uous. This current may be diverted through the con- 
ducting-cords, as already shown, by opening the switch 
fully; and the strength of the pulsations may be varied 
in the same proportion as their frequency, by varying the 
distance between the sliding-rods. 

It is often employed for medical purposes, and may 
be made as mild and smooth as required for the most 
delicate case, by a very slight separation of the sliding- 
rods, producing a correspondingly rapid discharge, or as 
powerful as the strongest nerves can bear, by a wider 
separation, giving a correspondingly slow discharge, 
with proportionally greater accumulated energy. It 
may be transmitted through any part of the body in- 
cluded between suitable electrodes, for any medical pur- 
pose which, in the opinion of the physician, may be 
required, as for instance the production of muscular 
action in paralysis. 

The direction of this current, when thus employed, is 



36 ELECTRICITY FOR EVERYBODY. 

often of great importance, the application of the positive 
electrode to the affected part giving relief, bnt the appli- 
cation of the negative electrode producing irritation. 

Brush Discharge. — A highly instructive and exceed- 
ingly interesting brush discharge may be produced be- 
tween the sliding-rods, when they are separated three or 
four inches and the switch fully opened, which can be 
seen best in a darkened room at night. Brushes of light 
from the knobs radiate toward each other with a hissing 
sound : that from the positive side having a reddish color 
and much greater prominence than the other, branching 
into a variety of fantastic forms j while that from the neg- 
ative side is less prominent and of a bluish color, and 
undoubtedly merely represents the concentration of the 
discharge from the opposite side, — the change of color in- 
dicating loss of energy in the discharge in overcoming 
the resistance of the air. 

The cause of this brush discharge is the comparatively 
slow movement of electric energy between the outer coat- 
ings of the jars, through the partially insulating kiln-dried 
wood of the base, producing corresponding slowness of 
electric movement between the inner coatings through 
the air, during which there is time for radiation of the 
discharge toward the central point and its concentration 
on the opposite knob. 

The spark, on the contrary, is the result of an instan- 
taneous discharge of electric energy through the air, cor- 
responding to a similar discharge through the closed 
switch j during which the narrow line of highly resisting 
air, through which this discharge occurs, is heated to in- 
candescence. The white light of the spark is therefore 
due to the intensity of molecular motion produced in this 
narrow air-line during an exceedingly brief instant ; and 



STATIC ELECTRICITY. 37 

the red and blue lights of the brush discharge to the 
much lower intensity of molecular motion diffused over a 
very much larger air-space, and occurring in a propor- 
tionally longer time : just as a small wire may be quickly 
heated to incandescence in the flame of a lamp, while the 
same quantity of heat, applied more slowly to a larger 
wire, would produce only a red heat; and, if applied 
near one end, this color would become darker toward 
the other end. 

Report. — The report which always accompanies the 
static spark discharge is due to the instantaneous, violent 
molecular motion of the air in the line of discharge. This 
line of air is the medium by which the electric energy 
travels, and its motion is believed to be in the form 
of transverse vibrations, which produce undulations, or 
sound-waves, in the surrounding air, similar to those 
which would be produced by the instantaneous vibration 
of the string of a musical instrument instantaneously 
checked. 

The old theory that this report is produced by a col- 
lapse of the air, such as occurs in the partial vacuum pro- 
duced by an explosion, is inconsistent with the theory of 
electricity being a mode of molecular motion, — the mo- 
tion, in this case, being that of the air itself ; the slight 
expansion produced by the sudden heating of this nar- 
row air-line, and the shrinkage from its comparatively 
slow cooling, being totally different from the instanta- 
neous displacement and collapse of a large body of air, 
produced by an explosion of gunpowder, dynamite, or 
steam, and quite insufficient to produce the report. 

Direction of Rotation. — The rotation of the revolv- 
ing plate, in this machine, must always be in the direction 
indicated by the arrow, so that the carriers, after receiv- 



38 ELECTEICITY FOR EVERYBODY. 

ing their initial charge from the insulated brushes, shall 
pass the insulated combs, and through them impart this 
charge to the jars, before passing the uninsulated combs 
and brushes by which the residual charges are dis- 
charged. Reversal of rotation would reverse this process, 
and the carriers, while passing the uninsulated combs 
and brushes, would lose the charge received from the in- 
sulated brushes, leaving only the residual charges to im- 
part to the jars, which would be insufficient to charge the 
machine. 

The brushes must touch only the raised centers of 
the carriers, and not the glass, to produce the best 
results. 

The Wimshurst Machine. — This machine, named after 
its inventor, was first described in January, 1883, while 
the application for the writer's first patent on the machine 
just described was pending. It is constructed, as shown 
in Fig. 11, with two glass plates, of equal size, mounted 
vertically, about a quarter of an inch apart, on insulating 
hubs, on two standards supported on a wooden base. 
These plates are made to rotate in opposite directions by 
two belts, one of which is crossed, which are connected 
with two driving-wheels mounted on one shaft. Each 
plate has on its outer surface a number of carriers made 
of tinfoil strips, which radiate from near its center, and 
have small raised brass disks attached to them. 

Two curved brass rods, A B and G D, are attached to 
the standards at the front and rear, in diagonal positions, 
as shown, and at right angles to each other, and each 
carries, at its extremities, two brass brushes, which make 
contact with the carrier disks and generate the initial 
charge. 

Two pairs of insulated horizontal combs, E and F, each 



STATIC ELECTRICITY. 



39 



pair connected with the inside coating of a Ley den jar, 
are mounted, as shown, so as to inclose opposite edges of 
the plates, extending toward their centers at the front 
and rear, with their teeth near the outer surface of each 
plate. 




Fig. 11. 

A curved discharging-rod is also connected with the 
inside coating of each jar, and extends upward over the 
plates, each rod terminating in a brass knob, one of which 
is much larger than the other. These knobs can be sepa- 
rated to any required distance, or brought into contact, 
by a rotary movement of the rods by the insulating 



40 ELECTRICITY FOR EVERYBODY. 

handles shown. The outer coatings of the Leyden jars 
are connected together under the base by copper wires. 

When the front plate is rotated in the direction indi- 
cated by the arrow on the right, and the rear plate in the 
direction indicated by the arrow on the left, any opposite 
pair of carriers on the same plate, as A and B, become 
oppositely charged by the friction of the brushes. If A, 
for instance, becomes positive, then B becomes negative. 
But as the two plates act inductively on each other, these 
conditions are reversed on the rear surface of the rear 
plate, G becoming negative and D positive. But as car- 
riers A and (7, thus oppositely charged, rotate toward 
each other, and likewise B and D, and are followed by 
the other carriers, above and below, the charge is continu- 
ally multiplied by induction, the upper front surface of 
the front plate becoming positive, and its lower front sur- 
face negative, while these relative conditions are reversed 
on the rear surface of the rear plate, and also on the op- 
posite inner surface of each plate with reference to its 
outer surface. 

As the upper front surface of the front plate moves 
downward past comb JE, it imparts its positive charge to 
the inside coating of its connected jar, and as the lower 
rear surface of the rear plate moves upward past comb JS, 
it also imparts its positive charge to the same coating. 
In like manner a negative charge is imparted to the in- 
side coating of the jar connected with comb .Ffrom the 
lower front surface of the front plate and the upper rear 
surface of the rear plate, the outside coatings of the jars 
becoming oppositely charged by induction, by a transfer 
of electric energy through the connecting wire. 

When the charge resulting from the difference of elec- 
tric potential produced in this way becomes strong enough 



STATIC ELECTRICITY. 41 

to overcome the resistance of the air between the knobs 
of the discharging-rods, a discharge occurs in the manner 
already described in connection with the last machine. 

The order in which the charge has been assumed to 
occur has been chosen arbitrarily, merely for convenience 
of description, and it is liable to occur in reverse order 
with the same direction of rotation and relative diagonal 
positions of the brushes. Bnt no automatic reversal can 
occur while the machine is in operation, as often happens 
with the machine last described. 

A reversal of rotation, with the brushes in the relative 
diagonal positions shown, would tend to produce equal- 
ity of potential, instead of difference, in all the gener- 
ating parts of the machine, and hence would not produce 
a charge. But if the relative diagonal positions of the 
brushes were reversed, then corresponding reversal of 
rotation would become necessary to produce a charge. 

Uses of Influence Machines. — Influence machines 
are extensively used to illustrate the principles of electri- 
city, and also for -medical purposes ; being employed not 
only to produce the static induced current for medical 
use, as already mentioned, but also to give an electric 
charge to a patient seated on an insulated platform. 

This charge may be given by connecting the patient, by 
one of the electrodes, with the inside coating of one of 
the Leyden jars, while a ground connection near the plat- 
form is made by the electrode connected with the inside 
coating of the other jar. The charge thus received is 
distributed over the entire surface of the body, and its 
effect is to equalize the vital functions; quickening the 
pulse, if abnormally slow, or making it slower, if ab- 
normally quick; acting as a sedative of abnormal ner- 
vous excitement, or increasing such excitement if ab- 



42 ELECTEICITY FOE EVERYBODY. 

normally low ; and equalizing the bodily temperature in 
a similar manner. Patients afflicted with nervous dis- 
eases, such as paralysis agitans (St. Vitus's ,dance), may 
be relieved in this way ; the same treatment is found to 
be beneficial for rheumatism also. 

The electric energy may be concentrated on any part of 
the body of a patient thus insulated and connected, by 
applying the electrode used for the ground connection 
to the required part ; sparks being drawn in this way 
through the clothing by means of a roller, ball, or point 
electrode, according to the nature and degree of electric 
concentration required. 

By means of an electrode consisting of a single point, 
or a cluster of points, brought within close inductive dis- 
tance of any part of the body, as the head or face, but 
not within sparking distance, a gentle breeze known as 
the electric wind, or souffle, may be produced, which has a 
very agreeable sedative effect; insulation of the patient 
receiving such treatment not being strictly necessary, 
though the effect is stronger with insulation, since there 
is no electric loss. 

Vacuum Tubes. — Closed glass tubes in which a partial 
vacuum has been produced are an important means of 
showing the relatively lower electric resistance of rarefied 
air as compared with air at the ordinary density, and 
thereby illustrating important electric principles. The 
best tubes for this purpose are those invented by Crookes 
and Geissler. The air in the Crookes tubes is reduced 
to about T ooiooo of its ordinary density, and that in the 
Geissler tubes to about 3-^00 of its ordinary density. 

The general construction of the Geissler tubes, which 
are made in a great variety of forms, is shown in Fig. 12, 
and consists usually of a small glass tube, bent into any 



STATIC ELECTRICITY. 



43 



convenient ornamental form, and inclosed within a larger 
one for security against breakage. Fine platinum wires 
are embedded in the glass, at 
each end of the larger tube, by 
which electricity can be trans- 
mitted through both tubes. 
When these wires are con- 
nected with the discharging- 
rods of an influence machine, 
a very beautiful discharge is 
transmitted, which fills the in- 
terior of the smaller tube, and 
is of a light reddish color ter- 
minating in a bluish color at 
its negative end, as in the brush 
discharge; various color-effects 
being produced by the com- 
position of the glass, or by in- 
closed gases, liquids, or solids. 
The most brilliant effects are 
produced by an intermittent 
current, like the static induced 
current described on page 35, 
or the faradic, described on 
page 112. 

This discharge, following the 
various convolutions of the 
smaller tube, may be three to 
six feet or more in length; 
and is easily transmitted this Fi g- 12 - 

distance through air at the density maintained in the 
Geissler tubes; while a discharge through air at the 
ordinary density, with the same electric pressure, may 




44 ELECTEICITY FOR EVERYBODY. 

not exceed the same number of inches. But in the 
higher vacuum of the Crookes tubes, -which are of some- 
what similar construction, electric resistance increases 
with the vacuum, for the opposite reason — that is, 
from a want of sufficient air as the medium of trans- 
mission. And if it were possible to produce a perfect 
vacuum, devoid of everything except the ether, it is 
doubtful whether transmission through it, except by in- 
duction, would be possible. 

The reddish color of the discharge in the Geissler tubes 
is due to the low resistance of the air and proportional 
diffusion of the charge and reduction of heat generated, 
as compared with the high resistance encountered by the 
discharge in air at the ordinary density, in which a nar- 
row line of air is heated to incandescence. 

Lightning. — It is a most remarkable instance of the 
slow development of electric science in former times, that 
thunder and lightning were not recognized as electric 
phenomena till after their identity as such, and the 
means of proving it, were suggested by Franklin, and 
subsequently verified by himself and others; his cele- 
brated kite experiment enabling him to obtain electric 
sparks from an insulated key connected with the wet kite- 
string, identical with those obtained from an electric 
machine, and to charge a Leyden jar with them. 

The electric charge of the thunder-cloud is acquired, in 
much the same way as that of an influence machine, by 
an initial charge multiplied by induction. Evaporation 
has been suggested as the probable means by which this 
initial charge is generated, experiment proving that elec- 
tricity can be generated in this way. It seems- probable 
also that the friction of vapor-laden air with the earth's 
surface, and elevated objects, as trees, rocks, and build- 



STATIC ELECTRICITY. 45 

ings, with which it comes in contact when moving as a 
wind, should be an additional means of electric genera- 
tion fully equal to that of evaporation, or perhaps su- 
perior to it. 

The separate infinitesimal drops of water composing 
this vapor become separately electrified, the charge ac- 
cumulating on their surfaces; and as these drops are 
condensed into larger drops, the extent of surface in pro- 
portion to volume is reduced, and the electric accumula- 
tion on this reduced surface proportionally increased. 
Two drops, for instance, condensed into one, have the 
same quantity of water and electricity as was contained 
in the two, but much less surface area on which this elec- 
tric charge is accumulated, and hence proportionally 
higher electric surface potential. These drops contin- 
ually attract smaller drops by their difference of poten- 
tial, and thus condensation, with increase of potential, 
proceeds rapidly, and a thunder-cloud begins to form. 

As this charged cloud is moved by the wind, it acts in- 
ductively on the earth's surface below it, and this surface 
acts inductively on it, the cloud becoming positive and 
the earth's surface negative ; aud thus the charge is in- 
ductively increased, in geometrical ratio, by continual 
multiplication into itself, in the same manner as the 
similar charge in influence machines is increased by the 
mutual induction of the plates; electric energy being 
continually attracted to the cloud from the surrounding 
air, and the same quantity repelled from the earth's sur- 
face below it. This accounts fully for the rapid forma- 
tion of the thunder-cloud, and the enormous electric po- 
tential which it acquires. 

When the difference of potential between the earth and 
the cloud becomes sufficient to overcome the resistance 



46 ELECTRICITY FOR EVERYBODY. 

of the air, the discharge which we call lightning occurs, 
usually from the cloud to the earth, taking the course 
of least resistance, which is usually between the cloud 
and some elevated object on the surface, preferably 
one which has a point or angle, or is a good electric 
conductor. 

Return Stroke. — The charge is not evenly distrib- 
uted in the cloud, electric energy tending to accumu- 
late at the point where there is the highest induction, as 
between an elevated object and that part of the cloud 
nearest to it, making distant parts relatively negative ; 
and when a discharge occurs, as above, this negative 
potential is instantly greatly increased, producing rela- 
tively positive potential in the earth below, which may 
result in such a difference of potential at this distant 
point as to cause a discharge from the earth to the 
cloud, termed the return stroke, shown theoretically in 
Fig. 13, which, like the downward stroke, follows the 
path of least resistance. Hence it is impossible to tell 
whether a stroke of lightning has occurred in a down- 
ward or an upward direction, the effect being the same 
in either case. This reaction may be such, even close at 
hand, as to produce sensible results, as when persons in 
the vicinity of an object struck by lightning feel the 
shock. 

The concentration of electric energy at a given point, 
previous to the discharge, is shown in Fig. 13 by the 
arrows in the cloud and in the earth, and also by the 
branches in the cloud leading to the main line of dis- 
charge; and the diffusion of this energy in the cloud, 
which follows the return stroke, is shown by similar 
branches leading from the line of discharge. 

The inductive influence of different thunder-clouds on 



STATIC ELECTRICITY. 47 

each other is the same as that between the cloud and the 
earth. There is always a difference of potential between 
them which attracts them toward each other, and this dif- 
ference constantly increases as they approach each other, 
till the electric strain is sufficient to overcome the resis- 
tance of the intervening air, when a discharge occurs. 
Such a discharge between two clouds increases the differ- 
ence of electric potential between each of them and other 
thunder-clouds in their vicinity, producing the series of 
discharges which often occur in rapid succession during 
a severe thunder-storm. 

Lightning occurs in the same manner as the electric 
discharge of the machine, producing incandescence in a 
narrow line of air, often three to five miles or more in 
length, as measured by the known distance between 
mountain-peaks. When the line of discharge is visible, 
it is called chain lightning, illustrated by the two photo- 
graphs of such discharges shown in Fig. 14; but when 
obscured by intervening clouds so that only the diffused 
or reflected illumination is seen, it is called sheet light- 
ning; and when this illumination arises from distant 
clouds below the horizon, as often happens on warm 
summer evenings, it is called heat lightning. But these 
various appearances all have the same origin. 

The crookedness observable in the line of discharge is 
doubtless due to the difference of resistance encountered 
at different points in the air, and the forked discharge to 
the mutual repulsion of air molecules charged to the 
same potential, and the attraction of the surrounding 
air, which is at a lower potential, similar effects being 
observable in the spark and brush discharges of the 
machine. 

It should be observed that the line of discharge has no 



48 ELECTRICITY FOR EVERYBODY. 

sharp returning angles, such as are usually shown in 
artificial representations 5 also that the branches extend 
in various directions like the branches of a tree, so that 
those extending from the observer appear much fainter 
than those extending toward him, the appearance of 
being on a flat surface being the effect of perspective. 
The apparent vertical discharge, as shown in the lower 
photograph, is also probably the effect of perspective, the 
discharge having probably occurred in a horizontal di- 
rection, parallel with the earth's surface, and above the 
light cloud which partly obscures it, the water in the 
distance, which it seems to strike, merely terminating 
the horizontal view. 

It is impossible to ascertain by observation the direc- 
tion in which the electric energy moves in the line of dis- 
charge, as even the longest discharge occurs in an in- 
finitesimally brief instant, — so brief that the entire line, 
which may be five miles or more in length, is seen at the 
same instant. We have a familiar illustration of this in 
a rapidly moving carriage-wheel, seen by a lightning- 
flash at night, which appears as if standing still, so that 
its separate spokes can be easily distinguished, which 
would be quite impossible if the flash occupied even 
the shortest perceptible period of time. Its apparent 
momentary duration is an optical illusion, — the impres- 
sion made on the retina of the eye remaining for a mo- 
ment after its cause has ceased ; the flash revealing the 
wheel to the eye, and instantly ceasing, like the snap- 
shot of a kodak, but infinitely quicker. 

Thunder. — The report which we call thunder is es- 
sentially the same as the report of the discharge in the 
machine or Leyden jar, and is produced in a similar 
manner, — not by the displacement and collapse of a 




Fig. 13. 




Fig. 14. 



STATIC ELECTRICITY. 49 

large body of air, as in an explosion, but by the instan- 
taneous vibration of a long, narrow line of air. For the 
electric discharge indicated by the loudest thunder, even 
when close at hand, has no effect on window-glass, 
which would be shattered by the air displacement and 
collapse produced by an explosion giving a similar 
report. 

The series of reports, decreasing in loudness, which 
usually follow each flash of lightning are attributed to a 
series of echoes between separate clouds, and also be- 
tween the clouds and the earth, the latter being probably 
the loudest, since the under surface of a cloud becomes 
denser and more even than its upper surface, and hence, 
like the surface of the earth below it, better adapted to 
produce these echoes. 

Lightning-rods. — The lightning-rod, proposed origi- 
nally by Franklin, is undoubtedly a most efficient means 
of protecting buildings against lightning, when properly 
constructed ; but when improperly constructed it is liable 
to become a fruitful source of danger. 

Copper is the best material for a rod, since it has the 
highest electric conductivity of any of the base metals; 
its conductivity being more than six times that of iron, 
and nearly equal to that of silver, which is the highest. 
The rod should be large enough, in solid cross-section, to 
carry the heaviest electric discharge which can occur, 
without risk of being melted by its heat, or having any 
part of it enter the building. Its form and relative quan- 
tity of surface, about which many erroneous opinions 
have been promulgated, are of very little electric impor- 
tance, since the charge is not confined to the surface, as 
was formerly supposed, but passes through its substance. 
Hence it may be solid or hollow, round, square, or flat, 

4 



50 ELECTRICITY FOR EVERYBODY. 

and its surface smooth or corrugated, provided it has 
sufficient massiveness and conductivity. 

It should be as free as possible from joints, which are 
liable to acquire high electric resistance from corrosion 
or imperfect construction, forming dangerous nodes from 
which electricity may escape into the building. Hence, 
wherever they are necessary, they should be so con- 
structed as to have no higher resistance than the other 
parts 5 soldering or, better still, electric welding, being 
the only sure means of accomplishing this. 

It should be attached to the building by conductors, 
not by insulators, as is often done, so that it may be 
in electric connection with every part, especially with 
masses of metal employed in construction, as gutters 
and cornices. And it should terminate above the roof in 
a sufficient number of points, sufficiently elevated to pro- 
tect every part of the building j the space so protected 
being usually estimated to be that of a cone whose apex 
is the highest point of the rod, and the diameter of whose 
base is twice its hight, there being no well-authenticated 
instance of damage by lightning within such a space. 
Hence, as many branches from the main rod as may be 
required by this rule should be erected on the roof, each 
having a main terminal point not so sharp as to be easily 
fused by a discharge, and connected with a circular clus- 
ter of sharper points a short distance below it. Chim- 
neys especially should be protected in this way, both on 
account of their elevation and the conductivity of the 
soot and ascending column of hot air and steam. The 
lower terminal should extend down to permanently moist 
earth, and there have branches soldered or welded to 
masses of metal. 

The protection afforded by the rod consists chiefly in 



STATIC ELECTRICITY. 



51 



its ability to prevent a disruptive discharge, by a gradual, 
silent discharge through its points, as illustrated by the 
similar discharge of a Ley den battery, described on page 
27, thus preventing the accumulation of a dangerous 
charge. 

The Aurora. — The electric appearance which has re- 
ceived the name of the aurora, from its resemblance to 
the morning dawn, originates in the vicinity of the polar 




Fig. 15. 

circles, and hence is called also the aurora polaris ; the 
southern aurora being known as the aurora australis, and 
the northern as the aurora borealis. Observation has 
been chiefly confined to the latter, which occurs within 
an irregular geographical belt about thirty degrees wide, 
extending from about north latitude 40° to 70° ; though 
in some parts of the western hemisphere it is sometimes 
seen as far south as latitude 22°, and in some parts of 
the eastern hemisphere as far north as latitude 77° ; its 
position in both hemispheres varying with the season of 



52 ELECTRICITY FOR EVERYBODY. 

the year, — its southern limit being reached near the equi- 
noxes, and its northern near the solstices. The center of 
this auroral belt is near the north magnetic pole, latitude 
70° 5' N., longitude 96° 46' W. from Greenwich. 

The general appearance of the aurora, shown in Fig. 15, 
is that of an arch of white light rising from the horizon, 
like the morning dawn, from which reddish streamers 
radiate upward, appearing and disappearing in rapid 
succession, in a series extending along the rim of the 
arch from one extremity to the other, often with an 
undulatory motion, the arch continually rising till the 
streamers sometimes reach the zenith. It assumes a 
variety of different aspects, often appearing either as 
a corona in the zenith, from which streamers radiate in 
opposite directions, or as curtains draped in curves, or as 
bands of reddish light spanning the heavens from east to 
west, or as concentric arches of white light rising from 
the horizon. 

Its apparent vertical position is an optical illusion, the 
effect of perspective, its actual position being always 
parallel to the earth's surface, the arch being the visible 
part of a great circular belt of white light, from which 
red streamers radiate in opposite directions, as seen in the 
corona when part of this belt reaches our zenith. Ob- 
servers in high northern latitudes, within this circular 
belt, see its inner rim toward the south, while observers 
in lower latitudes, outside of it, see its outer rim toward 
the north. 

Its hight is estimated to be about sixty-nine miles 
above the earth's surface : an estimate which may be ac- 
cepted as correct, if the rarity of the atmosphere at this 
hight is about the same as that of the Geissler tubes. 
But as the stratum of air in which it occurs is probably 



STATIC ELECTRICITY. 53 

many miles in thickness, the difference of atmospheric 
density between its upper and lower surfaces must vary 
considerably ; so that this estimate, if correct, would re- 
present only its average height. 

Cause of the Aurora. — This brings us to the cause 
of the aurora. Its electric origin is now fully established 
by the effect produced, during its prevalence, on various 
electric apparatus, especially on that pertaining to the 
telegraph. This effect becomes manifest in currents in 
the telegraph lines, often strong enough to operate the 
instruments without the battery current, when both ends 
of the line are connected with the earth ; or to produce 
such disturbance as to interrupt all telegraphic commu- 
nication throughout the whole country, and across the 
ocean ; heating the instruments, burning connecting wires, 
and igniting connected woodwork, and also lighting elec- 
tric lamps, — such occurrences being known as electric, or 
magnetic, storms. 

These currents are proved to be in the earth, and not 
in the atmosphere, for when the regular connection of the 
lines with the earth is interrupted, the disturbing cur- 
rents instantly cease ; and, of course, the battery currents 
also. 

The continual prevalence of electric currents in the 
earth, from warm to colder regions, has been proved by 
experiments on telegraph lines; such currents having 
been observed to flow from east to west during the morn- 
ing hours, when the temperature of eastern regions, 
warmed by the sun, is higher than that of adjacent west- 
ern regions cooled during the night; and from west to 
east during the evening hours, when these relative condi- 
tions of temperature are reversed ; the electric pressure 
varying as the relative difference of temperature. Well- 



54 ELECTEICITY FOR EVERYBODY. 

known laboratory experiments prove the same thing on a 
small scale, showing that electric currents are generated 
by difference of temperature, flowing from hot to cold 
parts of conductors ; the electric pressure varying as this 
difference. 

It is evident from this that electric earth-currents must 
flow from the torrid zone to the frigid zone, which, on ac- 
count of the great difference of temperature, must be pro- 
portionally stronger than the east and west currents. 
These currents must flow across the temperate zones, and 
be strongest between adjacent regions having the greatest 
difference of temperature; the high temperature of the 
torrid zone and low temperature of the frigid zones being 
comparatively uniform. And as these currents converge 
toward the poles, like the meridians, they must produce the 
highest electric intensity in those parts of the temperate 
zones adjacent to the polar circles, which, as has been 
shown, are the regions where the aurora is most prevalent. 

The prevalence of these earth-currents during the prev- 
alence of the aurora, as has been shown, proves that 
there is a very intimate relation between them, which 
must be attributed to electric induction. A stratum of 
dense, highly insulating air, many miles in thickness, lies 
between the highly rarefied air stratum of the aurora and 
the earth's surface ; and it is evident, from the nature of 
induction, as already explained, that electric currents in 
the earth, under this insulating air stratum, must pro- 
duce opposite currents in the highly rarefied air above, 
where the electric resistance is about the same as that in 
the Geissler tubes. 

These air-currents are shown in the streamers radiating 
from the auroral arch, which correspond in appearance 
and color to the discharge in the Geissler tubes; the 



STATIC ELECTRICITY. 55 

white light of the arch indicating the higher intensity of 
electric energy induced by the corresponding intensity in 
the earth below, due to the concentration of the earth- 
currents, as shown above. This concentration of electric 
energy corresponds to that in the positive charge on the 
interior coating of the Leyden jar; and the inductive 
effect seen in the auroral arch, to the negative charge ; 
electricity flowing from the arch, as shown by the stream- 
ers, just as it flows from the exterior coating of the jar, 
producing an effect similar to that in the Geissler tubes 
connected with these coatings, as already explained ; the 
insulating air corresponding to the insulating glass of 
the jar. 

Another reason for this higher intensity is found in the 
greater density of the insulating air stratum in the cold 
region under the auroral arch, which brings the auroral 
air stratum proportionally nearer to the earth's surface, 
increasing the effect of induction inversely as the square 
of the distance; so that, if this distance is reduced one 
half, for instance, the effect of induction becomes four 
times as great. 

The electric theory of the aurora as first proposed by 
Franklin ascribed its origin to the warm currents of air 
arising in the torrid zone, positively charged by evapora- 
tion, especially from the ocean, meeting the cold, nega- 
tively-charged air-currents from the frigid zones, and 
producing electric discharges in the rarefied air of the 
upper atmospheric strata. This theory has been accepted 
by leading electric writers, and if true, then the inductive 
effects described above must occur in reverse order, the 
earth currents being induced by the atmospheric currents. 

It is difficult to reconcile this theory with the fact that 
the principal air-currents, or winds, are confined to the 



56 ELECTRICITY FOR EVERYBODY. 

insulating atmospheric stratum, within five miles of the 
earth's surface, and more than sixty miles below the stra- 
tum usually assigned to the aurora ; the air above this 
lower stratum being so thin that winds are hardly per- 
ceptible. Hence, according to this theory, the aurora 
should occupy a much lower altitude than that assigned 
to it by any observer, whereas some assign to it an alti- 
tude of 120 miles above the earth's surface. 



CHAPTER III. 
Electeic Batteeies. 

Elementary Principles. — The simplest method of 
generating electricity for practical use is by means of 
the battery, called, by way of distinction, the voltaic bat- 
tery, after Volta, its original inventor, or the primary 
battery, to distinguish it from the secondary or storage 
battery. 

There are a great number of different kinds of these 
batteries, but, for our present purpose, only a few of the 
leading kinds which have come into general use need be 
described. They all generate electricity by chemical ac- 
tion, and have certain peculiarities of construction, com- 
mon to all, which it will be most convenient to describe 
first. 

The term hatter y is applied either to a single jar, or 
cell, containing the generating materials, or to a number 
of such cells connected together by electric conductors ; 
the latter being the more proper use of the term, though 
the former use is common. These materials are a fluid 
mixture, or solution, in which are partly immersed two 
solid bodies, as shown in Fig. 16, the combination re- 
sulting in chemical action and the generation of electri- 
city. And the variation in these simple materials, or in 
the manner of employing them, is what produces the 
different kinds of batteries. 

57 



58 



ELECTRICITY FOR EVERYBODY. 



The solid bodies are called electrodes, the one princi- 
pally affected by chemical action being called the gener- 
ating electrode, and the other the con- 
ducting electrode. The parts of these 
electrodes which project out of the 
fluid are called poles, and are distin- 
guished by the terms positive and neg- 
ative, as indicated by the plus and 
minus signs ; the positive pole, by 
which the electric current leaves the 
cell, as indicated by the. arrow on the 
right, belonging to the conducting 
electrode, and the negative pole, by 
which the returning current enters the 
cell, as indicated by the arrow on the 
left, belonging to the generating elec- 
trode. These electrodes are always 
carefully insulated from each other, 
so that the current must go through 
the fluid from the generating to the conducting elec- 
trode, and, after passing out by the positive pole and 
traversing the external circuit, return by the negative 
pole to the generating electrode. They are made of 
various materials, but zinc is almost invariably used 
for the generating electrode, and carbon is more gen- 
erally used for the conducting electrode than any other 
substance, copper being the next material in most com- 
mon use for this electrode ; silver, platinum, and mer- 
cury are also used, mercury being the only liquid thus 
used. 

Various kinds of fluid are employed, the principal 
kinds being solutions in water of sal-ammoniac, potas- 
sium bichromate, and copper sulphate; also nitric and 




Fig. 16. 



ELECTRIC BATTERIES. 59 

sulphuric acids diluted with water. The battery fluid 
contained in a cell may be of one kind only, or of two 
kinds partly separated by a porous cup, or in some other 
way, as by gravity, when one fluid is lighter than the 
other. This gives rise to the two kinds of cells, the one- 
fluid cell, in which both electrodes are immersed in the 
same kind of fluid, and the two-fluid cell, in which each 
electrode is immersed in a separate fluid. 

Polarization. — The construction of a battery cell 
would be a very simple matter, if there were nothing 
to interfere with the generation of electricity when the 
electrodes are immersed in the fluid and the circuit closed. 
A cell constructed with zinc and copper for the electrodes, 
and dilute sulphuric acid for the fluid, would then con- 
tinue in active operation till the strength of the acid was 
exhausted. But, unfortunately, an opposing force is 
developed by this action which soon stops it entirely, 
unless means are provided for its suppression. 

There is always in the water, and also in most of the 
other materials composing the various battery fluids, 
both oxygen and hydrogen. These elements are sep- 
arated by the chemical action ; the oxygen, going to the 
zinc or other metal composing the generating electrode, 
and uniting with it, forms an oxide, while the hydrogen 
goes to the conducting electrode, accumulates on its sur- 
face, and produces an electric pressure which opposes the 
electric current generated at the surface of the zinc by 
the chemical action just described. This hydrogen accu- 
mulation forms an opposing positive pole, and hence this 
effect is termed polarization ; and it is the various devices 
for the suppression of polarization, by preventing the 
accumulation of the hydrogen, which, more than any- 
thing else, has produced the great number of different 



60 ELECTRICITY FOR EVERYBODY. 

kinds of battery cells which have been invented, and con- 
stitutes the principal differences between them. 

One of the most effective means for suppressing polar- 
ization is to use, in the composition of the fluid, some 
chemical substance which is so rich in oxygen that there 
is enough of this element set free by the chemical action 
not only to unite with the zinc, but also with the hydro- 
gen, and prevent its accumulation. 

Another method often employed effectively, either 
alone or in connection with the above method, is to give 
the conducting electrode a rough surface, to which the 
hydrogen cannot adhere so easily as to a smooth sur- 
face, since a point has but little adhesion for any fluid, 
and hence a surface composed chiefly of points allows 
the hydrogen to escape rapidly through the liquid into 
the air, which it has a strong tendency to do, being the 
lightest of all gases, except the ether. 

The Smee Cell. — The first battery cell constructed 
on this principle was made by Smee, an English 
electrician, in 1840, and had for its conducting elec- 
trode a plate made either of silver 
plated with a rough coating of plat- 
inum, or of copper plated with a rough 
coating of copper, which was then 
plated with silver, to give it greater 
conductivity, and afterward with plat- 
inum, to protect it from the dilute 
sulphuric acid used for the fluid. This 
plate was suspended between two 

plates of zinc, so as to have the two 
Fig. 17. ^ ' 

rough surfaces exposed to the direct 

action of two zinc surfaces, as shown in Fig. 17, in which 

the zinc plates are marked z z and the silver plate s. 




ELECTRIC BATTERIES. 61 

Zinc-carbon Cells. — It was soon found that the 
rough-surface method of depolarization could be much 
more cheaply and efficiently carried out by the use of 
carbon for the conducting electrode than by the expen- 
sive method adopted by Smee ; carbon having not only a 
rough external surface like that of the Smee plate, but, 
being porous, a large internal surface is also brought 
into contact with the fluid. It has also the requisite 
conductivity for an electrode, when of sufficient cross- 
section, and, like the platinized surface of the Smee plate, 
is insoluble in acid. 

The carbon first used for this purpose was cut from 
the inside of gas-retorts, but this was very impure j and 
it is now prepared from pure carbon, which may be ob- 
tained from petroleum and other substances, and after 
being ground and made into a paste with some liquid 
carbon, as gas-house pitch, it is molded to the proper 
form and baked, going through various processes to give 
it the requisite consistence. 

The Law Cell. — The Law cell, shown in Fig. 18, is 
one of the most common cells of this kind. It is con- 
structed with a cylinder of pure carbon and a rod of pure 
zinc, attached to a close-fitting, insulating cover — the 
zinc being within the cylinder, so that its entire surface 
is exposed to the carbon surface. The great extent of 
carbon surface in proportion to zinc surface reduces the 
density of the hydrogen, which spreads over this carbon 
surface in a very thin film, from which the gas escapes 
rapidly into the air. In Fig. 19 is shown a double car- 
bon cylinder, a small cylinder being inclosed within a 
larger one, giving a proportionally greater extent of car- 
bon surface, which is used in a similar cell of this kind. 

The Law cell belongs to a class known as sal-ammoniac 



62 



ELECTEICITY FOR EVERYBODY. 



cells ; tlie fluid in this and other cells of this class being 
a solution of sal-ammoniac, about six ounces of which, 
finely pulverized, is dissolved in enough water to fill a 




quart cell about two- 
thirds full. As sal- 
ammoniac contains 
no oxygen to unite 
with the hydrogen, it does not assist in depolarization, 
which is therefore effected, in this cell, by the rough 
carbon surface only. 

It is claimed that there is no chemical action in any well- 
constructed sal-ammoniac cell, having materials of requi- 
site purity, except when the electric circuit is closed, and 
that consequently the electrodes can remain constantly 
in the fluid without injury. But when the circuit is closed, 
the zinc surface is attacked by the chlorine liberated from 
the sal-ammoniac, which corrodes it, forming zinc chlo- 



ELECTRIC BATTERIES. 



63 



ride, so that the zinc is eventually destroyed, and a new 
one required ; but pure carbon, like that employed in the 
Law cell, is not affected by the chemical action, and 
hence this electrode does not require renewal, but should 
occasionally be soaked in warm water to remove any 
impurities which may have accumulated. 

The Samson Cell.— This cell, shown in Fig. 20, be- 
longs also to the sal-ammoniac class, and is constructed 
on principles quite the reverse, in some respects, of those 




-- 



Fig. 20. 



followed in the construction of the cell just described. 
Instead of a small zinc rod inclosed within a large 
carbon cylinder, either single or double, it has a cylinder 
of sheet zinc inclosing a porous carbon cylinder of large 
cross-section, having a channeled surface, as shown in 
Fig. 21 ; thus giving a much greater extent of zinc sur- 
face in proportion to carbon surface than in the Law cell. 
This large generating surface is thus brought close to the 
conducting surface, reducing the electric resistance be- 
tween them, through the fluid, to the lowest practical 



64 



ELECTKICITY FOR EVERYBODY. 



limit, and proportionally increasing the electric efficiency 
of the cell. This internal resistance is still farther re- 
duced by the large cross-section of the carbon, and the 
channeling greatly increases the depolarizing external 
surface. 




Fig. 22. 



Fig. 23. 



The carbon cylinder is hollow, and filled with a mixture 
of crushed carbon and manganese binoxide, a substance 
which is rich in oxygen ; and some of this oxygen, being 
liberated by the chemical action, unites with some of the 
hydrogen, forming water, and thus assists in depolariza- 
tion, compensating for the smaller proportion of depolariz- 
ing surface as compared with that in the Law cell. 

The Leclanche Cells. — The first battery cell in 
which sal-ammoniac was used was invented by Leclanche, 



ELECTRIC BATTERIES. 65 

a French electrician, and is known as the Bisque Le- 
clanche cell. It is represented in Fig. 22, and cells of 
this kind are still in common nse. 

The conducting electrode is constructed with a porous 
cup of un glazed porcelain, in which is placed a carbon 
plate, surrounded with a mixture of crushed carbon and 
manganese binoxide, in about equal proportions, to which 
is added a little water. This cup is closed with Portland 
cement, except two small openings left for ventilation 
and the addition of water when required, and is placed in 
a glass jar, with a half -inch zinc rod, similar to that used 
in the Law cell, for the generating electrode, which is 
placed in a recess, as shown. 

The sal-ammoniac solution, which is placed in the glass 
jar, permeates the porous cup, and by its chemical action 
on the manganese binoxide liberates some of its oxygen, 
which unites with some of the hydrogen, and assists in 
depolarization, as already described ; the principal chemi- 
cal action being at the surface of the zinc, as in other 
cells. 

It was found that the porous cup added greatly to the 
electric resistance of the cell, proportionally reducing its 
electric energy. To remedy this, Leclanche invented the 
conducting electrode shown in Fig. 23, in which the por- 
ous cup is dispensed with, and the manganese binoxide, 
and other materials having important qualities, are ce- 
mented together, molded into prisms, and condensed 
under heavy pressure to increase their conductivity. Two 
of these prisms are attached to the carbon plate by stout 
rubber bands, as shown, each prism being so shaped as 
to leave an opening between it and the plate. And the 
cell having this electrode is called the prism, or pile, Le- 
clanche cell. 



66 ELECTRICITY FOR EVERYBODY. 

The internal resistance of the cell being greatly reduced 
by this construction, its electric energy is proportionally 
increased. The gradual disintegration of the prisms by 
the chemical action referred to as resulting in the pro- 
duction of oxygen, eventually destroys them, necessitat- 
ing their renewal from time to time; while the carbon 
plate to which they are attached, being indestructible, 
remains permanent, as in the Law cell. This disintegra- 
tion of the conducting electrode occurs in every cell in 
which it is composed in part of manganese binoxide or 
other substance decomposed by the chemical action. 

There are various other sal-ammoniac cells in use, as 
the Laclede, Microphone, Diamond Carbon, and various 
dry cells. A very important advantage in all cells of 
this class is their entire freedom from noxious fumes and 
from acid, which makes them especially desirable for ring- 
ing house bells, or any household use for which a battery 
current may be required. And as the electrodes remain 
inactive in the fluid, without injury, in all such cells, 
properly constructed, the cell is always ready for work 
the moment the circuit is closed by pressing the push- 
button or otherwise. 

Sal-ammoniac cells are very efficient for what is called 
open circuit work, where the circuit is closed for only 
brief intervals, giving time for the escape of the hydro- 
gen during the intervals of rest. But, like all one-fluid 
cells, they polarize by the accumulation of hydrogen, 
when employed too long at a time, and hence are not 
adapted to closed circuit work, where the current is 
employed for long intervals without intermission. 

Potassium Bichromate Cells. — In this class of zinc- 
carbon cells potassium bichromate is used in the fluid 
as a chemical depolarizing agent, the fluid being com- 



ELECTRIC BATTERIES. 67 

posed of 9 per cent, of this salt, 25 per cent, of sulphuric 
acid, and 66 per cent, of water, which are recommended 
as the best proportions, though they may be varied if 
desired. Oxygen, being liberated from the potassium 
bichromate by the sulphuric acid, unites with some of 
the hydrogen, forming water, as in the similar cases 
already described. 

Cells of this class have great electric euergy, and are 
especially adapted to work requiring a powerful battery 
current for a short time, and hence are preferred for 
laboratory, lecture room, and medical use. But as polar- 
ization is not wholly suppressed, and waste material ac- 
cumulates which obstructs chemical and electric action, 
agitation of the fluid, and the removal of the electrodes 
from it, or of the zinc alone, becomes necessary after 
a few minutes' work, to give the cell an opportunity to 
recuperate. Both these results are accomplished at the 
same time by plunge batteries, of which there are many 
different kinds, in which the electrodes are lifted out 
of the fluid, supported above it, and allowed to drip, and 
then lowered into it again by some convenient me- 
chanical device. 

The Grenet Cell. — The Grenet cell, shown in Fig. 24, 
belongs to this class, and is constructed with a zinc plate 
suspended between two carbon plates, so as to have two 
carbon surfaces exposed to the direct action of two zinc 
surfaces, and as close to them as practicable without con- 
tact, to reduce the electric resistance through the fluid to 
the lowest degree. The glass jar has a capacious base to 
hold a large charge of fluid, which shall not be soon ex- 
hausted, and a wide neck into which the zinc can be 
lifted by a sliding rod having sufficient friction to sup- 
port it, as shown in Fig. 25. As the fluid produces 



68 



ELECTRICITY FOR EVERYBODY. 



chemical action on the zinc when immersed in it, whether 
the circuit is opened or closed, this electrode must be 
lifted out of it when the cell is not in use. 

This cell, is very convenient for experimental work re- 
quiring only a single cell j but, for heavier work, cells 
are constructed with two or more zinc plates suspended 





Fig. 24. 



Fig. 25. 



between carbon plates in a similar manner, in jars with 
straight sides, both electrodes being raised or lowered as 
required, by some mechanical device. 

As the fluid used in this class of cells soon weakens 
with use, and is subject to slow chemical decomposition 
when not in use, which results in the deposition of a 
crystalline substance called chrome alum, freshly made 
fluid should be used when strong electric action is re- 
quired. 

Amalgamation of the Zinc. — As ordinary commercial 
zinc contains impurities which reduce the electric effi- 
ciency of battery cells by producing electric currents con- 
fined to the surface of the zinc, which do not circulate 



ELECTRIC BATTERIES. 



69 



through the external circuit, and as strictly pure zinc is 
too expensive for battery use, it is customary in these 
and many other cells to amalgamate the surface of the 
zinc from time to time, as may be required, with mercury, 
combined with some suitable acid which will make it 
adhere properly. This gives the zinc a surface better 
adapted to its work, and assists materially in suppressing 
this local action, as it is called, which interferes with it. 

The Edison-Lalande 
Cell. — This cell, shown 
in Fig. 26, is construct- 
ed with a plate of black 
oxide of copper suspend- 
ed between two plates 
of zinc, and the fluid 
is a solution of caustic 
potash in water. It has 
very low electric resis- 
tance, which gives it pro- 
portionally high electric 
energy, notwithstanding 
its comparatively low 
electric pressure. It is 
said to be free from polar- 
ization, local action, and 
noxious fumes, and does 
not require the removal 
of the electrodes from the 
fluid when not in use, as 
there is no chemical ac- Fi 

tion except when the 

circuit is closed. Hence it is well adapted to domestic 
use, and is also recommended for telegraph work. 




70 ELECTEICITY FOR EVERYBODY. 

As both the caustic potash and black oxide of copper 
are rich in oxygen, the depolarization is doubtless due to 
the liberation of this element by the chemical action, and 
its union with the hydrogen. 

Dry Cells. — Cells of the sal-ammoniac class are now 
extensively used, in which starch, or some similar ab- 
sorbent, is mixed with the fluid, producing a jelly not 
easily spilled. This is placed in a small cup made of 
sheet zinc, which is employed as the gen- 
erating electrode, and in its center is 
placed a carbon conducting electrode, as 
shown in Fig. 27. The cup is then per- 
manently closed with an insulating cement 
which electrically separates the electrodes, 
making a portable cell, the contents of 
which cannot be displaced in any position. 
These are known as dry cells, and when 
^# well constructed have a high degree of 
efficiency for open circuit work; and, be- 
g * ing small and portable, are very con- 

venient for physicians, lecturers, and others who require 
a strong battery of several cells, which can be easily and 
safely carried. But when the fluid charge is exhausted 
the cell is of no farther use, as it requires complete re- 
construction, the cost of which would be more than that 
of a new celL 

Two-fluid Cells. — One-fluid cells, such as have been 
described, are all liable to polarization on a closed circuit, 
no matter how perfect their construction, and hence are 
not so well adapted as two-fluid cells to work in which 
the circuit is closed for long intervals, as in many kinds 
of plating-, or in which it is in constant use for long 
intervals, with rapid alternate opening and closing, as in 




ELECTRIC BATTERIES. 



71 



large telegraph offices. Hence, for such work, two-fluid 
cells are preferred, being practically free from polari- 
zation. 

The Daniell Cell. — The first two-fluid cell was in- 
vented by Daniell, an English electrician, in 1836, and 
the main principles adopted in his cell have never been 
superseded, cells constructed according to his original 
method being still in use, while improved cells, con- 
structed on the same leading principles, are far more ex- 
tensively used than any other two-fluid cells, being con- 
sidered the best of this class. 

This construction is illustrated by Fig. 28, in which is 
shown, in a glass jar, a porous cup containing the zinc. 
This cup is inclosed within 
a copper cylinder having a 
vertical opening on one 
side, for the free circula- 
tion of the fluid, this cylin- 
der being the conducting 
electrode. Dilute sulphuric 
acid is placed in the cup, 
in contact with the zinc; 
and in the jar, in contact 
with the copper, is a solu- 
tion of copper sulphate, a 
salt composed of copper 
and sulphuric acid without 
hydrogen. 

The chemical action decomposes the sulphuric acid in 
the porous cup, zinc uniting with it, displacing its hy- 
drogen, and forming zinc sulphate. The copper sulphate 
in the outer jar is also decomposed, and its copper de- 
posited on the copper cylinder, liberating its sulphuric 




Fig. 28. 



72 ELECTRICITY FOR EVERYBODY. 

acid ; which unites with the displaced hydrogen through 
the porous cup, and is changed to ordinary sulphuric 
acid, which is decomposed and unites with the zinc, as 
before, displacing more hydrogen. Hence there is never 
any free hydrogen in the cell, as it is absorbed by the 
acid destitute of it the moment it is liberated from the 
acid in combination with it, and is thus kept constantly 
employed in transferring sulphuric acid from the decom- 
posed copper sulphate to make the zinc sulphate, and 
hence cannot do mischief as an idle polarizer, as in other 
cells, copper instead of hydrogen being deposited on the 
copper cylinder, and zinc sulphate accumulating around 
the zinc. 

Crystals of copper sulphate are placed in a perforated 
copper cup, shown on the right, and these dissolve slowly 
and keep the solution replenished, supplying fresh cop- 
per sulphate in place of that decomposed by the chemical 
action ; the consumption of this material, and also of the 
zinc, being nearly as great when the cell is idle as when 
it is in action. 

The electric pressure generated by this cell is only a 
very small fraction more than a volt, as mentioned in the 
definition of that unit on page 19 ; hence it is the stan- 
dard usually referred to as representing the volt, where 
strict accuracy is not required. 

Gravity Cells. — The electric resistance of the porous 
cup employed in the Daniell cell, and the local action 
produced by the material of which it is composed, led to 
the invention of similar cells in which it is dispensed 
with. This resistance is due to the reduction of cross- 
section in the fluid between the copper and the zinc by 
the intervention of the cup, this cross-section being rep- 
resented in the cup only by the fluid permeating its 



ELECTRIC BATTERIES. 



73 



pores, which is but a small fraction of the entire fluid 
cross-section. 

As the solution of zinc sulphate, which surrounds the 
zinc, is lighter than the solution of copper sulphate, which 
surrounds the copper, the method has been adopted of 
placing the zinc in the upper part of the cell and the 
copper in the lower part, as shown in Fig. 29 ; the separa- 
tion of the fluids by gravity 
bringing each electrode into 
contact with its own fluid, 
with full fluid cross-section, 
and corresponding low re- 
sistance between them, thus 
dispensing with the porous 
cup, with its limited cross- 
section and corresponding 
high resistance. Connection 
with the copper electrode is 
made by a copper wire, in- 
sulated from the zinc and 
fluid surrounding it by a 
covering of gutta-percha or 
India-rubber. Crystals of copper sulphate are placed in 
the bottom of the cell, around the copper electrode, for the 
same purpose as in the Daniell cell. 

After the cell has been set up and put in action, suffi- 
cient time must elapse for the formation of zinc sulphate 
and separation of the fluids before full action is attained j 
and agitation of the fluids, which would result in mixing 
them, must be avoided. Total separation is not practi- 
cable, a small percentage of the copper sulphate rising 
into contact with the zinc and producing copper pen- 
dants from it, after the fluid has been in use for some 




Fig. 29. 



74 



ELECTRICITY FOR EVERYBODY. 



time. These pendants must be removed before they be- 
come long enough to reach the lower fluid. 

Cells of this construction require but little care, and 
are extensively used for telegraphing, to which they are 
well adapted, large batteries of them being often em- 
ployed for this purpose. 

Bunsen and Grove Cells. — The Bunsen cell, shown 
in Fig. 30, is a two-fluid cell constructed with zinc and 
carbon electrodes ; a carbon prism being placed in a 

porous cup containing nitric 
acid, and this cup inclosed 
within a slotted zinc cyl- 
inder, well amalgamated, 
which is placed in a glass 
jar containing dilute sul- 
phuric acid. 

Oxygen is liberated from 
the nitric acid in sufficient 
quantity to absorb all the 
hydrogen and produce com- 
plete depolarization ; and 
the comparatively low re- 
sistance of this acid adds greatly to the electric energy 
of the cell, which is one of the most powerful in use. 
The Grove cell is of similar construction and equal 
energy, but has a strip of platinum for its conducting 
electrode, which is much more expensive than the car- 
bon prism. 

Both cells emit noxious red fumes, due to the chemical 

decomposition of the nitric acid, which are so irritating 

and unwholesome that these cells are now but little used. 

Battery Connections. — Cells are connected so as to 

form batteries by connecting their electrodes together 




Fig. 30. 



ELECTRIC BATTERIES. 



75 



with conductors, which are usually copper wires. A bat- 
tery thus formed may consist of any number of cells re- 
quired for the work for which it is intended, from two 
to several hundred; but they should all be of the same 
kind, as it is not advisable to have cells of different kinds 
in the same battery. 

There are two methods of making this connection, 
known respectively as the series method, and the parallel 
method. In the series method, illustrated by Fig. 31, the 




Fig. 31. 

generating electrode of each cell is connected with the 
conducting electrode of the adjacent cell; and in the 
parallel method, illustrated by Fig. 32, all the generating 
electrodes are connected together and likewise all the 
conducting electrodes. 

The quantity of electric energy generated is precisely 
the same by either method, but the effects produced are 
very different. The series method gives high electric 
pressure and proportionally small volume of current, 
while the parallel method gives low electric pressure and 
proportionally large volume of current. 



76 



ELECTRICITY FOR EVERYBODY. 



The electric pressures of the three cells shown in Fig. 
31 are added together by the flow of the current from 
cell to cell, producing three times the pressure of a single 
cell ; but as this current encounters the electric resistance 
of each cell, the resistance is increased in the same pro- 
portion as the pressure, so that the current's volume is 
equal only to that from a single cell. 

In the three cells shown in Fig. 32, the three carbon 
electrodes being connected together, and likewise the 




Fig. 32. 



three zinc electrodes, each set has only the same elec- 
tric potential as that of a single electrode, and hence the 
difference of potential between the positive and nega- 
tive poles, which produces the electric pressure, is only 
the same as that between the poles of a single cell; 
and the whole combination of electrodes, poles, and fluid 
in the three cells is just the same as that of a single cell 
three times the size of any one of them. 

But the increase in cross-section of electrodes and 
fluids, by this combination, produces a corresponding 
reduction in the electric resistance, and hence a propor- 



ELECTRIC BATTERIES. 77 

tional increase in current volume, which is three times 
that of a single cell, while the electric pressure is only 
the same as that of a single cell. 

As the total electric energy is represented by the elec- 
tric pressure and current volume multiplied together, it 
is evident that three times the current volume multiplied 
by the pressure of a single cell, as in the parallel arrange- 
ment here represented, gives just the same electric energy 
as three times the electric pressure multiplied by the cur- 
rent volume of a single cell, as in the series arrange- 
ment — the pressure being represented in volts and the 
current volume in amperes. And the same rule will 
apply to any number of cells. 

The difference between these two methods of battery 
connection may be illustrated by the following example: 
Let a tank filled with water have a faucet at bottom 
through which the water can flow. Now let another 
tank, three times the hight, have a faucet of one third 
the size. The pressure at this faucet will be three times 
as great as at the other, but the volume of current which 
can flow through it in a given time will be just the same, 
because the resistance is increased, by reduced size, in the 
same proportion as the pressure. This represents the 
series method. 

Now let three tanks of the same hight as the first one 
be placed side by side, on the same level, and connected 
together at bottom by pipes, and a faucet three times the 
size of the first be attached to one of them. The pressure 
at this faucet will be just the same as that at the first 
one, but the volume of water which can flow through it 
in a given time will be three times as great, because the 
resistance, reduced by increase of size, is only one third 
as great. This represents the parallel method. 



78 ELECTRICITY FOR EVERYBODY. 

These different methods of battery connection are quite 
important in practical electric work, and may be varied 
to any extent required, by combining both methods in 
the same battery, as by having two or more groups of 
parallel-connected cells joined in series, or two or more 
groups of series-connected cells joined in parallel. 

The electric pressure of the battery must be propor- 
tioned to the electric resistance of the circuit. If this 
resistance is high, as in a long telegraph line, the electric 
pressure must be made proportionally high, so that there 
shall be enough strength of current left to operate the 
instruments after overcoming the resistance of the circuit. 
Hence the series method is preferred for this purpose. 
But if the circuit resistance is low, and a current of large 
volume is required, as in electric plating, the parallel 
method is preferred; or such a combination of the two 
methods may be employed as shall give the requisite 
pressure and current. 

Comparison between Large and Small Cells. — 
The electric pressure of battery cells varies from half a 
volt to about one and three quarter volts. This pressure 
depends on the difference of potential between the poles, 
which is produced by the materials of which the cell is 
composed and their relative arrangement, and not by 
the size of the cell. A cell no bigger than a lady's 
thimble has just as great electric pressure as one the size 
of a gallon jar, whose materials and construction are the 
same. 

This may be illustrated by the pressure of water, or 
any other liquid, which depends entirely on the hight of 
the column, and not on its size in cross-section. A col- 
umn of water in a tank ten feet high, and one square 
foot in cross-section, has just the same pressure as a 



ELECTRIC BATTERIES. 79 

column in a tank of the same hight which is a hundred 
square feet in cross-section. And if the two tanks be 
connected together at bottom by a pipe, the small col- 
umn will counterbalance the large one, so that the water 
will stand at exactly the same level in each. 

In like manner, if the small cell referred to above be 
so connected with the large one that its pressure shall 
oppose that of the large one, the two pressures will 
exactly counterbalance each other, so that there will be 
no current in the connecting circuit. 

But it is evident that a small cell cannot have the 
same durability or constancy as a large one of the same 
construction, though it has the same electric pressure, — 
its material being more rapidly exhausted, proportionally, 
by the chemical action, just as the water in the small 
tank would be more rapidly exhausted than that in the 
large one, by the same outflow. 

Also, as the electric resistance of conductors varies 
inversely as their cross-section, that is, decreases in the 
same proportion as the cross-section increases, it is evident 
that the resistance of a large cell is as much less than 
that of a small cell of the same construction as the cross- 
section of its electrodes and fluid is greater. Hence its 
volume of current, with the same pressure, being in- 
creased in the same proportion as the reduction of re- 
sistance, is proportionally greater. 

Storage Batteries. — The apparatus commonly called 
the storage battery is also known as the accumulator, and 
as the secondary battery, this last term being employed 
to distinguish it from the primary battery, and these var- 
ious terms being applied either to a single cell, or to a 
collection of cells electrically connected together. These 
batteries are employed to accumulate, or store, a given 



80 ELECTRICITY FOR EVERYBODY. 

quantity of electric energy, estimated by the number of 
hours required to discharge it at a given rate, and are 
not, in any sense, generators of electric energy. 

The electric energy thus stored is usually generated 
by a dynamo, but may also be generated by a primary 
battery, and produces certain chemical changes in the 
material contained in the cell during the storing process, 
or charging, by which electric energy is accumulated. 
And during the discharge these chemical changes are 
reversed, electric energy flowing from the cell, till the 
materials are restored to their original chemical condi- 
tion, when the discharge ceases. 

The Plante Cell. — Various attempts to accomplish 
electric storage by means of gases and otherwise were 
made by different electricians during the first half of the 
present century, but the first practical storage cell was 
invented by Plante, a French electrician, in 1859, who 
discovered the special adaptability of lead to this purpose. 
His cell was constructed with two lead plates, insulated 
from each other and immersed in water acidulated with 
sulphuric acid contained in a glass jar. These plates 
were connected respectively with the opposite poles of a 
primary battery, by which the chemical changes pertain- 
ing to the charge were produced. 

After each charge, given in this manner, he discharged 
the cell by connecting the plates together by a copper 
wire, and then charged them in reverse order, and by 
continuing this process for several months, increasing 
the charge continually and allowing a period of rest after 
each discharge, he produced a cell which, when charged, 
had a thick coating of lead dioxide on the positive plate, 
and of spongy lead on the negative, but when discharged, 
had a coating of lead sulphate on both plates. During 



ELECTRIC BATTERIES. 



81 



the discharge a powerful electric current flowed through 
the connecting wire, by which iron rods were melted and 
other interesting laboratory experiments performed. 

The Faure Cell. — Faure, another French electrician, 
shortened this process by coating the plates with a paste 
made of lead oxide and sulphuric acid, which, by Planters 
process of alternate charging and discharging, could be 
changed in a few days to lead dioxide on the positive 
plate and spongy lead on the negative. 

This cell was subsequently improved by substituting 
for the supporting lead plates lead grids, like that shown 
in Fig. 33, each hole being narrower at its center than at 
each surface, as indi- 
cated by the shading, 
so that the paste, when 
pressed into it, took 
the form of a rivet, 
and was thus held in 
place. The lead oxide, 
known as red lead, or 
minium, was used for 
the positive plates, and 
the light-colored lead 
oxide, known as lith- 



ri i Jt 



IL 










A 


I 


............. 


J ■■ - [utn|_j]_ 


finH 




3~~ 


_m _ : 








~1 




1 ! 


"Hn : 











^H 






liiiiuiiiiiMil 




j i 










— 


1 


"T" 


■"" 


1 




t 






.__ 












.__ 


J_ 


.1 














MHI HI ■! ■! HI Ml HI HI Ml ■ ■ Hi 

■lilHIHlHHlHHHHHHHll 





Fig. 33. 



arge, for the negative plates, and the water was acidu- 
lated with 36 per cent, of sulphuric acid. 

The cells thus improved have come into general use, 
and are made of different sizes, each having a number of 
these plates. Fig. 34 illustrates the construction and the 
mode of connecting them together to form a battery. 
The plates are supported vertically by lead lugs which 
rest on opposite edges of a glass jar, space being left 
below for the circulation of the fluid. The positive plates 



82 



ELECTRICITY FOR EVERYBODY. 



alternate with the negative and are separated from them 
about three sixteenths of an inch by hard-rubber insula- 
tors, the outside plates being both negatives, so that there 
is always one more negative than positive, giving an equal 
number of active surfaces of each kind, as the two outside 
surfaces are inactive. 




Fig. 34. 

One of the lugs on each plate has a short copper rod 
attached to it, as shown, which fits loosely into a hole in 
a transverse copper bar, one of which is supported on 
each side of the cell, as shown ; the plates being so placed 
that the lugs with rods attached alternate with those 
without rods on each side, so that all the positive plates 
are electrically connected together by the rods and trans- 
verse bar on one side, and allthe negative plates in a 
similar manner on the opposite side ; the holes in the bars 
containing mercury to maintain perfect electric contact. 



ELECTRIC BATTERIES. 83 

When the cells are connected together as a battery, as 
shown, the lugs with rods, in each cell, come opposite 
those without rods in the adjacent cell, the rods from 
each cell occupying alternate holes in the transverse bars, 
so that the positive plates of one cell are electrically con- 
nected with the negative plates of the adjacent cell by 
the transverse bar supported between them, as shown. 
By this arrangement any plate can be lifted out for in- 
spection or repairs without disturbing the others, as 
shown on the right in Fig. 34. 

The number and size of the plates vary in different 
cells, and also their thickness; plates eighth of an inch 
thick and quarter of an inch being used, the positives 
being a little thicker than the negatives. The negatives, 
not being subject to oxidation like the positives, have 
much greater durability, one year of constant use being 
the longest time for which manufacturers guarantee the 
positives. Portable cells are made with hard-rubber 
vessels, furnished with covers. 

Most of the Faure cells in use have lead connections, 
without joints, which are not liable to corrosion by the 
acid fumes and creeping salts, like the copper connections 
here described. 

The American Cell. — Plates constructed like those 
in the Faure cell are liable to warp or buckle, especially 
when the discharge is continued too long, on account of 
the unequal expansion, on opposite surfaces, of the lead 
sulphate which forms during the discharge ; the lead plate 
bending easily, while the grid bars, being short and rigid, 
cannot yield so as to make room for the expansion of the 
paste. It is also difficult to obtain lead oxide of uniform 
chemical composition, the ordinary commercial article 
being liable to great variation in its composition. 



84 



ELECTRICITY FOR EVERYBODY. 



These faults have led to the invention of plates of a 
different construction both mechanical and chemical, in 
the cell known as the American, shown in Fig. 35. Its 
plates constructed as shown in perspective in Fig. 36, and 

in cross-section at A in 
Fig. 37, are made of pure 
lead, and deeply grooved 
on both surfaces. The ac- 
tive material, lead peroxide 
in the positive plates and 
spongy lead in the nega- 
tives, fills these grooves. 
The peroxide is formed 
from the lead itself, as in 
the Plante cell, but much 
more rapidly, requiring 
only two days for its for- 
mation instead of several 
months. This is done by a 
special process, the nature 
of which is a business secret, as well as the composition 
of the fluid employed for this purpose. The peroxide 
formed in this way, being of perfectly uniform compo- 
sition throughout, is claimed to have much higher elec- 
tric efficiency than is possible to be obtained from paste, 
as in the Faure cell. The negative plates are formed from 
the positives by chemically changing the peroxide to 
spongy lead by the electric current, as in the Plante and 
Faure cells. 

The plates of both kinds are about T \- of an inch in 
thickness, and when assembled in the cell, as shown in 
Fig. 35, the positives alternate in position with negatives 
and are insulated from them by hard rubber separators 




Fig. 35. 



ELECTEIC BATTERIES. 85 

constructed as shown at B in Fig. 37, leaving a space 
about T 3 g- of an inch wide for the free circulation of the 
fluid. 

The plates in each set are electrically connected to- 
gether, as shown, by lead bars soldered to lead clamps, 
strips of lead extending from the bars for connecting the 
cells in a battery; and are supported on projections at the 




Fig. 36. a Fig. 37. B 

bases of the separators; and the two sets are held to- 
gether by stout rubber bands. The fluid is composed of 
one part sulphuric acid and five parts pure water. 

The Chloride Accumulator. — The invention of this 
cell, which is of recent origin, is due to Payen, a French 
electrician. Its construction is illustrated by Figs. 38 
and 39, Fig. 38 showing one of the negative plates after 
its chemical formation. The little circular tablets, or 
pastilles, as* they are called, form the active material, and 
are prepared from a mixture of lead chloride and zinc 
chloride, from which, after fusion by heat, they are cast 
in molds ; each having a hole in the center, as shown, and its 
outer edge being convex, and therefore wider at the center 
than at each surface. These pastilles are then arranged in 
a mold, by being placed on pins through the central holes, 



86 



ELECTRICITY FOR EVERYBODY. 



and the supporting plate, composed of lead and a small 
percentage of antimony, cast round them; the melted 
metal being forced into the mold under powerful air pres- 
sure, so as to make the plate dense and free from air- 
holes, the convex edge of each pastille being inclosed by 
the concave groove which it forms in the inclosing plate, 
so as to be firmly held in place. 

A number of these plates are then placed in a tank 

containing a solution of 
zinc chloride, in contact 
with solid plates of zinc, 
which alternate with 
them, where they remain 
forty-eight hours. This 
combination is virtually 
a primary battery, the 
electric action of which 
is confined to the cell it- 
self j and its effect is to 
remove both the zinc 
chloride and the chlorine 
of the lead from the 
pastilles, leaving in them 













Fig. 38. 



only a porous crystalline structure of pure lead, sup- 
ported by the solid lead-frame. The pores in the pas- 
tilles are at right angles to the surface of the plate, and 
can easily be seen by a magnifying glass 5 a few of them 
being roughly represented by the small holes surround- 
ing the central hole. A connecting lug of lead is fused 
on each plate, and the plates to be used as negatives are 
then complete. 

The pastilles for the positive plates are made of lead tape 
with cross projections on one surface, and are rolled into 



ELECTRIC BATTERIES. 87 

flat disks, like cloth tape, the spaces between the pro- 
jections producing little holes, or pores, through them, and 
they are softened and made more porous by a short im- 
mersion in a bath of nitric acid. They are concave at 
the edges, and being wider at the surfaces than at the 
centers, are held in the plate like rivets. 



Fig. 39. 

The plates are then assembled in tanks containing di- 
lute sulphuric acid, positives and negatives alternating, 
and being insulated from each other, but each kind con- 
nected together by conductors, outside the fluid, in two 
separate sets ; and are subjected for several days to a 
powerful dynamo current, which flows constantly from 
the positive set to the negative j by which lead peroxide 



88 ELECTRICITY FOR EVERYBODY. 

is formed upon the lead tape of the positives, while the 
spongy lead of the negatives remains unchanged. The 
positives and negatives are then assembled in a cell as 
shown in Fig. 39, the adjoining plates being separated 
from each other by thin wooden boards or by strips of 
hard rubber. 

The Edison Storage Cell.— Mr. Edison has recently 
developed a storage cell containing very different ele- 
ments from those already described, and designed with 
particular reference to producing a cell which should be 
as light as possible. The electrodes in this new cell are 
iron and superoxide of nickel, and the electrolyte is a 20 
per cent, aqueous solution of potassium hydrate. 

When discharging the iron is oxidized and the super- 
oxide of nickel is reduced to a low oxide ; when charging 
the iron oxide is reduced to spongy metallic iron, and the 
nickel oxide is oxidized to a superoxide. 

The oxide of nickel is used in a finely divided form, 
commingled with a conducting substance such as flake 
graphite in order to improve the conductivity of the mass. 
The iron is also used in finely divided form commingled 
with a similar conducting substance. Both of these active 
materials are compressed into thin cakes or briquettes. 
Each briquette is placed in a shallow, closely fitting nickel 
plated box of thin perforated sheet steel, and this is then 
closed by a cover of similar material. These boxes con- 
taining the active material are then forced into holes in 
nickel plated steel grids under hydraulic pressure, so as 
to make plates of great mechanical strength. 

Electric Pressure and Rate of Discharge. — The 
electric pressure of the lead storage cells is about two 
volts each, and the volume of current far greater than 
that usually obtained from ordinary primary cells, on ac- 



ELECTRIC BATTERIES. 89 

count of the relatively greater number and larger size of 
the plates, the low internal resistance, and entire absence 
of polarization. This volume of current can be varied to 
any required extent by varying the resistance of the ex- 
ternal circuit, producing proportional variation in the 
rate of discharge. A cell which can furnish a current of 
one ampere for 300 hours is said to have a storage capac- 
ity of 300 ampere-hours ; but, by varying the resistance 
of the circuit, such a cell can be discharged in one hour 
with a current of 300 amperes, or in ten hours with a 
current of 30 amperes, or in thirty hours with a current 
of 10 amperes, and so on. 

Batteries of any required size can be formed by con- 
necting cells together, either in series or in parallel, or 
by a combination of both methods, so as to furnish cur- 
rent of sufficient electric pressure and volume for electric 
lighting, or the operation of machinery by the electric 
motor. But notwithstanding the adaptation of storage 
batteries to work of this kind, they have not yet fulfilled 
the expectations entertained in regard to them ; the direct 
use of current from the generator, wherever obtainable, 
being more practical and economical. 

Electrolysis. — The decomposition of a chemical com- 
pound by the electric current, which occurs in the charg- 
ing of a storage battery, in the manner described, is 
known as electrolysis, a process which is employed in the 
arts for various purposes, especially for the deposition of 
metal in electroplating, electrotyping, and the electric re- 
fining of metals and their separation from their ores. 

It consists in transmitting a current of electricity, ob- 
tained from a battery or a dynamo, through a bath com- 
posed of a solution of the substance to be decomposed, 
by which its constituent elements are separated. Two 



90 ELECTRICITY FOR EVERYBODY. 

electrodes are employed, as in batteries, one of which is 
connected with the positive terminal of the electric cir- 
cuit, and called the anode, and the other with the neg- 
ative terminal, and called the cathode; and the electric 
current, as it traverses the bath, decomposes the solu- 
tion, one or more of its elements being deposited on the 
cathode and the others on the anode. 

In electroplating, the articles to be plated are employed 
as the cathode, the anode usually consisting of one or 
more plates of the metal to be deposited, and the bath 
containing some chemical salt of the same metal, dis- 
solved in water. This solution being decomposed by the 
current, the pure metal is deposited on the articles to be 
plated, while the other constituents of the salt, being set 
free, combine with the metal of the anode, forming a 
fresh supply of the salt, which is dissolved in the bath, 
replacing that which was decomposed. 

The electrotype process is similar. Impressions of the 
cuts or type to be copied are taken on plates composed 
of beeswax and graphite, which, after being properly 
prepared, are immersed in a solution of copper sulphate, 
and connected with the negative terminal of the electric 
circuit, at a distance of about two inches from anode 
plates of pure copper, connected with the positive termi- 
nal. The sulphate being decomposed by the current, its 
copper is deposited on the cathode plates, and its sul- 
phuric acid, being thus set free, unites with the copper of 
the anode plates and thus renews the supply of copper 
sulphate. 

When the copper deposited has attained the requisite 
thickness, it is stripped from the plates and given a thin 
coat of solder on the reverse surface, over which is 
poured type-metal, which is thus made to adhere, form- 



ELECTRIC BATTERIES. 91 

ing plates about one eighth of an inch thick, which are 
then mounted on wooden blocks. 

Metals are refined in a similar manner, the crude metal 
being used as the anode, and pure metal as the cathode, 
the bath containing a solution of some salt of the metal. 
Pure metal, taken from the solution, is deposited on the 
cathode plates by the current, and replaced by metal 
taken from the anode plates, which are thus gradually 
dissolved and replaced by similar plates of crude metal; 
the deposit being stripped from the cathode plates when 
it has acquired sufficient thickness. Copper refining is 
accomplished in this way on a very extensive scale. 

The separation of aluminum from its ore is now 
accomplished exclusively by this process. Carbon is 
employed both for the anode and cathode, and the 
aluminum ore, mixed with other substances, is fused 
at a red heat, in steel crucibles, and forms the bath from 
which the pure metal is deposited on the cathode by the 
electric current. The materials in the bath are kept 
fused constantly, fresh ore being added as required, and 
the pure metal, which sinks to the bottom in a melted 
mass, removed as it accumulates. 

Electrolysis in Medical Practice. — Electrolysis is 
also employed in medical practice for medicating diseased 
parts internally ; the process being known as cataphoresis. 
The medicine is applied to the surface of the affected part 
by a sponge or plate electrode, connected with whichever 
pole of the battery will produce its deposition in this part : 
and being usually a compound, it is decomposed, and each 
of its elements being transmitted through the tissues to 
the electrode for which it has an electrochemical affinity, 
a certain portion is deposited during transmission, and 
retained. 



92 ELECTRICITY FOR EVERYBODY. 

If, for instance, iodine is to be deposited in the diseased 
part, potassium iodide, which is a compound of potassium 
and iodine, may be used, and should be applied to the 
diseased part by the negative electrode, while the positive 
electrode is in contact with some other part of the body ; 
because iodine, being what is known in electrolysis as an 
electronegative element, or anion, goes to the positive elec- 
trode, while potassium, being an electropositive element, 
or cation, goes to the negative electrode. But if the ele- 
ment to be deposited in the diseased part were electro- 
positive, then the medicine should be applied by the 
positive electrode. 

Electric Cautery. — The battery current is also em- 
ployed for electric cautery, by which abnormal tissue is 
destroyed; and, for this purpose, electrodes are con- 
structed with fine platinum wires of suitable shape, at- 
tached to insulating handles. These wires, having high 
electric resistance, are instantly heated to a red or a white 
heat by a strong current, and such electrodes can be em- 
ployed for various cauterizing purposes, limited chiefly 
to diseases of the throat and nose ; furnishing also, at 
a white heat, light to guide in their application in the 
interior cavities of these organs. 



CHAPTER IV. 
Magnetism. 

Elementary Principles. — Magnetism, like electricity, 
was known to the ancients five or six hundred years 
before the Christian era, having been discovered in a 
certain black stone, first found in Magnesia, a country of 
Asia Minor, which was therefore called the magnet stone. 
This stone, which is a species of iron ore, has the property 
of attracting iron, and also of pointing to the earth's 
poles, when balanced so as to have free motion. Hence 
this last property has been called polarity, and from it 
has originated the name lodestone, that is, leading stone, 
which has been given to the stone. 

Both these properties can be given to iron or steel 
rubbed with this stone, iron soon losing them, but steel 
retaining them permanently; and, in this way, steel mag- 
nets, and needles for the compass used by mariners, sur- 
veyors, and civil engineers, were at first made. Various 
metals, as well as iron and steel, can acquire these prop- 
erties, especially nickel and cobalt, but only in a very 
limited degree ; and it is believed that they pertain to all 
bodies, the earth itself having been found to be a great 
magnet, with its north and south magnetic poles, which 
attract the opposite poles of the steel magnet or compass 
needle. The north magnetic pole is in latitude 70° 5' X., 
longitude 96° 46' "W., as stated on page 52; and the 
south magnetic pole at about latitude 73° S., longitude 



94 ELECTRICITY FOR EVERYBODY. 

154° E., its exact location having never been accurately 
determined. 

Magnetism is one of the many forms in which energy 
manifests itself through matter as its medium, and, like 
electricity, it is believed to be a mode of molecular 
motion, propagated by vibrations of the molecules and 
undulations of the ether. Hence we find, in different 
substances, magnetic conductivity and resistance, similar 
to electric conductivity and resistance ; and we have also 
magnetic induction, magnetic potential and difference of 
potential — magnetic influence emanating from magnet- 
ized bodies as electric influence emanates from electrified 
bodies. 



TTTTTT 



/ ^ J ^ — \~ rr— r—i 



\ \ ''''/ //--— s\\M 11// / / / 

^ \ V x\\V ' "/^""^V ;///////■/ / / 

. _ j^_~- — _ -_ -f^s ^wwi/ftV/ \\\\m\\i!hk^ j^-_^r r— — -_^__ _ 

"~ _ — — —jt "jr^^ ///mmun^J^Vz^ C~ — —- ~~ 



','//M§ i > v oV- v- ', / '"' • * \\\ v 

' / i » \ wV-T---^/ //I I \ 



Fig. 40. 

Magnetic Lines op Force. — The existence and po- 
sition of the magnetic lines of force, representing this 
influence, may be made manifest by a very simple experi- 
ment. Place a sheet of stiff paper over a steel bar mag- 



MAGNETISM. 95 

net, and dust iron filings over it, tapping the paper 
gently, and the filings will arrange themselves in con- 
formity with the position of the lines of force, as shown 
in Fig. 40, or rather, will be moved into this position by 
the magnetic force. Now if it were possible to make the 
filings adhere properly in any other position of the paper, 
without dropping off by their own weight, a similar 
result would be obtained at any angle in which the paper 
might be placed while parallel to the magnet. From 
which it is evident that this flat figure is a cross-section 
of a spheroidal figure, represented by the lines of force 
which inclose the magnet. 

These lines, which are the result of magnetic in- 
duction in the space surrounding the magnet, appear to 
emanate from each end and curve toward the opposite 
end; but it is believed that, in reality, they emanate 
from one end, which has positive magnetic potential, and 
curve to the other, which has negative, by virtue of the 
difference of potential between the ends, the return cir- 
cuit being through the magnet, in the opposite direction. 

The Earth's Magnetism. — The shape of the earth is 
similar to that of the above figure, and lines of magnetic 
force circulate round it in a similar manner, from one 
of its magnetic poles to the other. Hence a straight 
magnet, or magnetic needle, which has a free hori- 
zontal motion, is forced into a north and south posi- 
tion conformable to these lines, and we call the end 
which points north its north pole and mark it JV, and 
that which points south its south pole, and mark it 8. 
But the polarity of each is opposite to that of the earth's 
pole toward which it points; for each pole of a magnet 
attracts that pole of another magnet which has opposite 
polarity, but repels the pole which has similar polarity. 



96 ELECTRICITY FOR EVERYBODY. 

When such a needle has a free vertical motion, its 
position conforms to that of the lines of force in a simi- 
lar manner, tending constantly to assume a vertical posi- 
tion when moved in the direction of either of the earth's 
magnetic poles, and becoming vertical at each pole, but 
tending to assume a horizontal position when moved 
toward a great circle midway between these poles, which 
is the earth's magnetic equator, and becoming horizontal 
at this equator. The vertical angle assumed by the 
needle at any point is called its dip or inclination, for 
that point. The needle's north pole dips in the north- 
ern hemisphere, and its south pole in the southern 
hemisphere. 

Agonic Line. — As the needle always points to one of 
the earth's magnetic poles, it is evident that it can also 
point to the adjacent geographical pole, that is, directly 
north and south, only when on a meridian which passes 
through both these poles, and that there can be only one 
such meridian. This meridian is known as the agonic 
line, or line of no angle, because the needle makes no 
angle with this line, while at every point east or west of 
it, the needle, pointing only to the magnetic pole, declines 
from a true north and south position, making the angle 
known as its declination, this declination being eastward 
when the needle is west of this line, and westward when 
east of it. 

The agonic line now passes through the United States, 
near Charleston, S. C, Toledo, O., and the west end of 
the Straits of Mackinaw. Hence, the compass needle on 
a vessel sailing from Chicago to Buffalo shows con- 
stantly decreasing east declination till the Straits of 
Mackinaw are reached, when it points directly north, and 
constantly increasing west declination from that point to 



MAGNETISM. 97 

Buffalo j these variations occurring in reverse order on 
the return trip. 

The position of this line is slowly shifting continually, 
with corresponding variation of declination. It reached 
its eastern limit, a short distance east of Washington, 
D. C, in 1797, and has since been moving westward. It 
will probably reach some point a short distance east of 
Chicago during the last half of the next century, and 
then move eastward again for a corresponding length 
of time. 

Both dip and declination vary considerably at different 
points $ hence lines of equal dip and equal declination, as 
drawn on magnetic maps by connecting such points 
respectively, show great irregularity, which must be 
ascribed to various local causes which produce variation 
in the earth's magnetism. And as the total magnetic 
intensity at any point is the result of the combined 
effects of dip and declination, this intensity also shows 
corresponding irregularity. 

Steel Magnets. — Steel bars, or compass needles, of 
any convenient size or shape, when properly tempered, 
are easily magnetized permanently by contact with a 
magnet. The usual method of accomplishing this is to 
place the bar or needle which is to be magnetized in a 
horizontal position, and placing the opposite poles of 
two bar magnets in contact on its center, the outer end 
of each being elevated at a convenient angle, draw them 
apart to the opposite ends of the bar and bring them to- 
gether again at its center a number of times alternately, 
stroking each side in this way an equal number of times, 
and quitting at its center. Another, and much more 
effective method, is to place the bar or needle inside a 
spiral coil of insulated copper wire, through which a 



98 



ELECTRICITY FOR EVERYBODY. 






strong current of electricity is then transmitted, by which 
it will be permanently magnetized. 

Magnets made in the form of a horseshoe, or the letter 
U, as shown in Fig. 41, are the best for many practical 
purposes. The two poles being thus 
brought near each other, the magnetic 
energy is concentrated on a small 
space which it traverses from one pole 
to the other, so that both poles can be 
employed for the same purpose, fur- 
nishing twice the energy of one. 

Steel magnets retain their magnet- 
ism for an indefinite length of time, 
unless heated to a white heat, or sub- 
jected to violent concussion, either of 
which may destroy it ; but it becomes 
8 ' ' impaired in the course of years, espe- 

cially in straight magnets or compass needles, which re- 
quire to be remagnetized from time to time to maintain 
requisite efficiency. By placing a piece of soft iron 
across the poles of a U magnet, as shown in Fig. 41, this 
magnetic loss is greatly reduced. The iron having high 
magnetic conductivity, the lines of force circulate through 
it freely, while this circulation is greatly impeded by the 
high magnetic resistance of the insulating air, and the 
magnetic energy thus impaired. This piece of iron is 
called the keeper or armature, from its ability thus to pro- 
tect the magnet against magnetic loss j and it becomes a 
magnet during its connection, having poles opposite to 
those of the magnet, at the points of connection. 

Portative Force. — The lifting power of a steel mag- 
net, which is a result of its attraction, is called its por- 
tative force, and is much stronger in a (J or horseshoe 



MAGNETISM. 99 

magnet than in a bar magnet, since both poles can be 
employed to sustain a weight attached to the armature. 
A magnet may thus sustain several times its own weight. 
By increasing the weight gradually, day by day, the por- 
tative force may be increased, but this increase is lost if 
the weight becomes so great as to separate the armature 
from the magnet. 

Effect of Breaking a Magnet. — If a magnet is cut 
or broken into two or more pieces, each piece becomes a 
separate magnet, with north and south poles in the same 
relative positions as in the original magnet, as shown in 
Fig. 42. But if the pieces be pressed closely together, their 



"&£ 



N«S N 



Fig. 42. 

poles disappear, leaving only the two original poles. 
Which shows that the magnetic energy traverses the 
magnet constantly from one end to the other j so that 
the number of poles may be considered infinite, all ar- 
ranged in the same relative position as the end poles — 
there being two of opposite polarity on opposite sides 
of any cross line, the relative polarity of which is not 
changed by the breaking. 

Consequent Poles. — It is possible, however, to mag- 
netize a bar oppositely in alternate sections, and thus 
produce a magnet in which the polarity of each alternate 
section is reversed, producing what are called consequent 
poles ; two north poles being in contact at one sectional 
junction, and two south poles at the next, and so on al- 
ternately, as if the sections were separate magnets joined 
together by their similar poles. 

LOfC. 



100 ELECTRICITY FOR EVERYBODY. 

Magnetic Attraction and Repulsion. — North and 
south polarity being regarded simply as positive and 
negative magnetic potential, as already stated, the same 
principle is found in magnetism as in electricity 5 differ- 
ence of potential producing attraction, and equality of 
potential producing repulsion. Hence either pole of 
a magnet attracts that pole of another magnet having 
opposite polarity, by virtue of this difference of potential, 
but repels that pole having similar polarity, by virtue of 
equality of potential ; a north pole and a south pole at- 
tracting each other, but two north poles or two south 
poles repelling each other • while either pole attracts un- 
magnetized iron or steel, and is attracted by it, on account 
of difference of magnetic potential. 

Electromagnetism. — It is remarkable that the inti- 
mate relationship now known to exist between electricity 
and magnetism was unknown till 1819, when the dis- 
covery was made by Oersted of Copenhagen that the 
magnetic needle can be deflected by the electric current 
into a position at right angles to the current ; the direc- 
tion in which its opposite poles are deflected depending 
on the direction in which the current flows. This dis- 
covery marks one of the most important epochs in the 
progress of electric science, opening the way for that 
wonderful electric development which has since been 
achieved, chiefly through that branch of electric science 
known as electromagnetism, the foundation of which was 
thus laid. 

Deflection op the Magnetic Needle by the Elec- 
tric Current. — Oersted's experiments are illustrated by 
Fig. 43, which shows, at A, B, C, and D, the four different 
positions which a balanced magnetic needle tends to 
assume when placed parallel to a wire through which an 



MAGNETISM. 



101 



electric current is flowing in the different directions in- 
dicated by the arrows; its poles being deflected in op- 
posite directions as the current flows from right to left, 
or from left to right, under or over the needle. By 
comparing A with C, and B with D, it will be seen that 
the needle assumes the same position when the current 




Fig. 43. 

flows under it in the opposite direction to that in which 
it flows over it. Hence when the current flows round it 
lengthwise, in opposite directions above and below, as at 
E and F, it is deflected with twice the force, the under 
current deflecting it in the same direction, in each case, 
as the upper current. 

By placing the wire in any other relative position to 
the needle, the same deflective effect is obtained; the 
needle always tending to assume a position at right 
angles to the direction of the current. Ampere gave this 
very simple rule for ascertaining the direction in which 
either pole is deflected. Imagine a little human figure, 
with its face toward the needle, traversed by the current, 



102 



ELECTRICITY FOR EVERYBODY. 



which enters at its feet and leaves at its head; its ex- 
tended left hand will always point in the direction in 
which the north pole is deflected, the sonth pole being of 
course deflected in the opposite direction. 

If the wire incloses the needle as a spiral coil, through 
which, viewed endways, the current circulates in the 
same direction as watch-hands, move, then, according 
to Ampere's rule, the north pole will be turned, from 
the observer, and the south pole toward him ; but if the 
direction of the current is reversed, the direction of the 
poles will be reversed also. 

If an unmagnetized steel bar or needle is magnetized 
in this way, as already explained, its polarity will be per- 
manently established in accordance with this rule. A 
soft iron bar, or needle, will be temporarily magnetized in 
a similar manner during the transmission of the current, 
acquiring its magnetism almost instantly when the cur- 
rent flow begins, and losing it as quickly when this flow 
ceases. 

Electromagnets. — Magnets so constructed as to be 




Fig. 44. 



temporarily magnetized in this way are called electro- 
magnets. Their construction is illustrated by Fig. 44. 
The spiral winding shown at A being the reverse of that 
shown at B, the spiral flow of the current is the reverse, 



MAGNETISM. 



103 



though its general direction is from right to left in each 
magnet, as indicated by the arrows. Hence, according to 
Ampere's rule, the little figure's left hand would indicate 
a north pole at the left in A and at the right in B. If 
each magnet, wound in this way, were bent into the form of 
a (J, as shown at G and D, the polarity of G would be the 
same as that of A, and the polarity of D the same as that 
of B. But if the general direction of the current were 
reversed in each magnet, so that it flowed from left to 
right, the polarity would be reversed. Hence the relative 
polarity of the poles, in any electromagnet, depends on 
the direction of the winding and the general direction of 
the current. 

Of course the wire in a U or horseshoe magnet is al- 
ways wound after the magnet is bent into proper form, 
as in other magnets j but it must be wound as shown at 
G or D, the wire crossing to the 
opposite side of the bend, otherwise 
the end poles would both have the 
same polarity, and there would be 
consequent poles at the bend, 
whose polarity would also be the 
same, but opposite to that of the 
end poles. 

There are usually a number of 
layers of this wire, which is 
wrapped with insulating material 
and closely wound like thread on 
a spool ; in fact, it is often wound 
on spools, which are afterward placed on the limbs of 
the magnet, as shown in Fig. 45. 

Magnet Core.— The iron part of an electromagnet is 
called its core, which should be made of the very best 




Fig. 45. 



104 ELECTRICITY FOR EVERYBODY. 

quality of soft iron, capable both of acquiring and losing 
its magnetism in the shortest time ; quick loss being as 
important as quick gain for most practical purposes, in 
which magnetic gain and loss usually alternate in rapid 
succession. The quantity of wire should be properly 
proportioned to the quantity of iron in the core, and 
should be just sufficient to produce magnetic saturation 
of the iron. Wire in excess of this is not only a wasteful 
incumbrance, but reduces the magnetic efficiency by in- 
creasing the electric resistance. The size of the wire and 
the number of times it should be coiled round the core 
depend entirely on the purpose for which the magnet is 
intended ; the pressure of the electric current varying in 
nearly the same proportion as the number of coils, and 
its volume as the size of the wire, and the magnetism, up 
to the point of saturation, varying in nearly the same 
proportion. But both pressure and volume must be 
adapted to the requirements of the electric circuit with 
which the magnet is connected. 

Electromagnets are far more powerful in proportion 
to their size than steel magnets. They may be of any 
required size, and are often made very large and massive 
in the construction of electric apparatus in which they 
are employed, as dynamos and motors, sometimes weigh- 
ing several tons. 

Solenoids. — A coil of wire through which an electric 
current is flowing shows magnetic properties similar to 
those of an electromagnet, but much weaker than those 
of a similar coil having a soft iron core. Such a coil, if 
suspended so as to have a free horizontal motion, as 
shown in Fig. 46, will assume a north and south position, 
and its poles will be attracted by the poles of a magnet 
or coil having opposite polarity, but repelled by those 



MAGNETISM. 



105 




Fig. 46. 



having similar polarity, like a magnetic needle. Coils 
made to illustrate this principle are usually shaped 
like a tube, as shown in 
Fig. 46, and are therefore 
called solenoids, the word 
solenoid meaning tube- 
like. 

The reason why the 
magnetism of an electro- 
magnet is so much 
stronger than that of a 
solenoid is because the 
iron core, on account of 
its high magnetic conduc- 
tivity, absorbs the mag- 
netic lines of force, and permits their free circulation, 
while, in the solenoid, they encounter the high resistance 
of the insulating air. 

Ampere's Theory of Magnetism. — Since a current 
of electricity, circulating in a wire coil, produces magnet- 
ism either in the coil itself or in an iron or steel bar in- 
closed within it, as shown above, Ampere inferred that 
such currents are in constant circulation in different direc- 
tions round the molecules of iron and steel and other 
metals capable of acquiring magnetism, and that the 
magnetizing process causes these currents all to circulate 
in the same relative direction, producing the magnetic 
effects ; this direction remaining permanent in steel, but 
being only temporary in soft iron, in which the irregular 
circulation is resumed as soon as the magnetizing process 
ceases. 

These currents, in a magnetized bar, would evidently 
circulate in opposite directions on adjacent sides of the 



106 



ELECTRICITY FOR EVERYBODY. 




Fig. 47. 



molecules, as shown in Fig. 47, in which the little circles 
represent the molecules, round which the currents cir- 
culate in the direction shown by the arrows ; hence they 
would all neutralize each other in the interior of the 

bar, leaving only the surface 
currents to circulate round 
it, as shown, just as they do 
in the coils of an electro- 
magnet, thus accounting for 
the permanent magnetism of 
steel magnets, round which, 
according to this theory, elec- 
tric currents are in constant 
circulation. 

Ampere's theory is not in- 
consistent with the more re- 
cent theory, already given, that magnetism is a mode of 
molecular motion, the magnetizing process, according to 
the latter theory, producing harmony of vibration among 
the molecules, while, according to Ampere's theory, it 
produces harmony of electric circulation round them. 
But there is no reason why the magnetic vibration should 
interfere with the electric circulation, while it is not im- 
probable that harmony of vibration may produce har- 
mony of circulation by bringing all the molecules into 
the same relative position. 

The magnetism of the earth has been attributed to the 
circulation of east and west currents round it continu- 
ously in the same direction, that is, from any given point, 
on one side, and toward the same point on the opposite 
side. But the existence of currents circulating in this 
way has never been established, while the east and 
west currents, which have been observed, circulate in 



MAGNETISM. 107 

the same direction on opposite sides, from the side ex- 
posed to the sun's rays to the opposite side ; and there- 
fore the magnetizing effect of each current is neu- 
tralized by the opposite magnetizing effect of the other, 
both tending to produce opposite poles at the same points 
north and south, as shown by Ampere's rule. For it is 
evident that, as the earth revolves, any point on its sur- 
face has an east to west current for twelve hours, and a 
west to east current for the next twelve, alternately, as 
explained on page 53 ; hence, when a point on one side 
has an east to west current, a point diametrically opposite 
to it has a west to east current. 

Magnetism Generating Electricity. — As electricity 
generates magnetism, so magnetism generates electricity. 
If a steel bar magnet be suddenly thrust into the interior 
of a wire coil, a transient current of electricity will be 
generated in the coil, and when the magnet is withdrawn, 
a similar current, flowing in the opposite direction, will 
be generated. If the magnet were given a constant mo- 
tion, in and out alternately in rapid succession, a corre- 
sponding series of these transient currents would flow 
through the coil alternately in Opposite directions. 

The direction in which each of these alternate currents 
would flow would depend on the relative direction of the 
magnet's poles, in accordance with Ampere's rule. A 
current produced by the entrance of the magnet's north 
pole first would be the reverse of that produced by the 
entrance of its south pole first. 

If a bar of soft iron were inclosed within the coil, the 
approach of a steel magnet to the end of this bar, and its 
subsequent withdrawal, alternately, would generate elec- 
tric currents in the coil in a similar manner, their relative 
direction, alternately, depending on the pole employed in 



108 ELECTRICITY FOR EVERYBODY. 

this way ; a current produced by the approach of a north 
pole being the reverse of that produced by the approach 
of a south pole. 

An electromagnet or a solenoid coil can be employed in 
the same way as a steel magnet for these various experi- 
ments, producing similar results. If a straight bar elec- 
tromagnet be placed within the coil, being insulated from 
it, an electric current transmitted through the magnet's 
coil will induce a transient current in the opposite direc- 
tion in the outer coil, and when the current in the mag- 
net's coil is interrupted, another transient current will be 
induced in the outer coil, which will now in the opposite 
direction to that of the first transient current, and hence 
in the same direction as the current in the magnet's coil. 
By opening and closing the circuit of the magnet's coil in 
rapid succession, in this way, a series of these transient 
currents, flowing alternately in opposite directions, can be 
induced in the outer coil. 

A similar result can be produced by alternately weaken- 
ing and strengthening the current in the magnet's coil, 
which can be done by connecting the terminals of this 
coil by a wire through which a portion of the current can 
be diverted. By alternately opening and closing this 
short circuit, a full current, at one instant, and a partial 
current, at the next, traverses the coil alternately, induc- 
ing an alternating current in the outer coil, propor- 
tionally weaker than that induced by the opening and 
closing of the main circuit. 

Induction Coils. — Coils constructed on the above 
principles are known as induction coils, the construction 
of which is illustrated by Fig. 48. The inner coil, called 
the primary, is composed of a few layers of coarse wire, 
which inclose the soft iron core, and the outer coil, called 



MAGNETISM. 



109 



the secondary , is composed of many layers of fine wire, and 
is insulated from the primary coil. 

Lines of force from the current transmitted through 
the primary coil, circulating through the secondary coil, 
induce the transient currents described j and as each turn 
of the wire in the secondary coil comes within this induc- 
tive influence, the electromotive force, or electric pressure, 
varies as the number of turns. But as the length of the 




Fig. 48. 

wire, and therefore its resistance, varies also as the num- 
ber of turns, and the volume of current varies as the 
resistance, it is evident that as the electric pressure is 
increased by increasing the nnmber of turns, the volume 
of the induced current is proportionally reduced by the in- 
crease of resistance. Hence, in this way, a primary cur- 
rent of large volume and low pressure can be transformed 
into an induced current of small volume and propor- 
tionally high pressure. 

The two binding posts, C and D, in Fig. 48, are con- 
nected with the terminals of the primary coil, and the 



110 ELECTRICITY FOR EVERYBODY. 

posts A and D with the battery, as shown. Post A is 
connected by a wire with B, and to post B is attached a 
steel spring called a vibrator, which makes contact with 
the point of an adjusting screw attached to post G. 
Therefore the battery current can be transmitted from A 
to B, through the spring to G, through the primary coil 
to D, and thence back to the battery. Posts F and G are 
connected with the terminals of the secondary coil. 

To the outer extremity of the vibrator is attached a 
little soft iron armature, which comes close to the end 
of the iron core of the primary coil 5 and when the bat- 
tery current is transmitted, this armature is attracted by 
the magnetism of the core, and the spring pulled away 
from its contact with the screw in post G, opening the 
circuit at that point. The opening of the circuit inter- 
rupts the current, thus demagnetizing the core, and the 
spring flies back into contact with the screw, closing the 
circuit again. Thus the circuit is automatically opened 
and closed alternately, the opening being technically 
called the break, and the closing, the make,. 

The length of the vibrations is adjusted by the screw 
in G; and as the waves of current induced in the sec- 
ondary coil correspond to these vibrations, their fre- 
quency can be controlled in this way, and, to a certain 
extent, their strength also, as each wave is either allowed 
to attain its full force during a long vibration, or is 
checked by a short vibration before attaining its full 
force. 

The core is usually composed of a bundle of soft iron 
wires, to prevent the formation of eddy currents, to 
which solid cores are liable; the wires being soldered to- 
gether at each end. It is inclosed by a copper tube, 
called a shield, which can be drawn out to any required 



MAGNETISM. Ill 

extent by the handle shown at E. This tube intercepts 
the mutual inductive action between the primary coil 
and core, an electric eddy current being induced in the 
tube itself, and thus weakens the induced current in the 
secondary coil, which can be regulated in this way, its 
strength being increased as the shield is drawn out, and 
reduced as it is pushed in. In some coils the current is 
regulated by a similar movement of the core itself, and 
in others by the movement of the primary coil, an elec- 
tromagnet being employed to operate the vibrator. The 
vibrator is also constructed and operated in different 
ways. 

The transient current induced in the secondary coil by 
the opening of the primary circuit has much greater 
electric pressure than that induced by its closing ; which 
is due to the fact that a current is induced between the 
adjacent turns and layers of the wire in the primary coil 
by what is called self-induction, which flows in opposition 
to the battery current at the instant the primary circuit 
is closed, but in the same direction as the battery current 
at the instant the primary circuit is opened. Hence the 
battery current at break has far greater pressure than at 
make, and its inductive effect on the secondary coil is 
proportionally greater. This inductive effect becomes 
manifest in a bright spark between the terminals of the 
secondary coil when brought near each other, similar to 
that of an influence machine, while the induced current 
at make has not sufficient pressure to produce a spark in 
coils of the ordinary size, and only a weak one in the 
largest coils. 

These sparks vary in length, from a small fraction of 
an inch to several feet, in proportion to the size of the 
coil. The largest coil in the world, that of Spottiswoode, 



112 ELECTRICITY FOR EVERYBODY. 

an English electrician, produces sparks 42 J inches in 
length when operated by a battery of fifty Bunsen cells. 
It has 280 miles of wire in its secondary coil, and 660 yards 
in its long primary coil. It has also a shorter primary 
coil, by which shorter, thicker sparks are produced. 

Induction coils are extensively used in medical prac- 
tice, the induced current being applied by handles, sponge 
electrodes, and other apparatus attached to flexible con- 
ducting cords connected with the terminals of the sec- 
ondary circuit, as shown at the posts F and G. 

This current is known as the faradic, and is similar 
to the static induced current, already described, though 
not identical with it, and is employed in medical practice 
for similar purposes. 

These coils are also nsed for various laboratory experi- 
ments illustrating the principles of electric science, such 
as electric transmission through vacuum tubes. They 
are also used to produce the sparks by which the gas is 
lighted in churches and audience halls, the spark being 
transmitted through the gas by a short break in the 
circuit at each burner. The primary coil alone is gen- 
erally preferred for this purpose, being simpler, cheaper, 
and less liable to accidental injury. 

Electric Bells. — One of the most common uses of 
the electromagnet is to ring the electric bell. The con- 
struction of this simple apparatus is shown in Fig. 49. 
The clapper of the bell is attached to a soft iron arma- 
ture A, supported near the poles of the electromagnet 
B, by the spring C. This spring makes contact with'an 
adjusting screw at D. The coils of the magnet are con- 
nected with the battery circuit by the binding posts E 
and F- 7 and this circuit passes through the spring G and 
screw at D. 



MAGNETISM. 



113 



Therefore, when the battery 
current is transmitted by clos- 
ing the circuit by the push 
button G, the armature is at- 
tracted by the magnet, caus- 
ing the clapper to strike the 
bell. This attraction pulls the 
spring away from the screw, 
opening the circuit at that 
point, and interrupting the 
current, and the magnet being 
thus demagnetized, the attrac- 
tion of the armature ceases, 
and the spring flies back into 
contact with the screw, pulling 
the clapper away from the 
bell, and the circuit being 
thus closed again, another 
stroke follows. Thus, by the 
alternate opening and closing 
of the circuit in rapid suc- 
cession, the bell is made 
to ring. The vibra- 
tions of the 




Fig. 49. 



spring can be adjusted by the 
screw to the strength of the mag- 
netizing current. 



CHAPTER V. 

Dynamos. 

Evolution of the Dynamo. — It was shown in the 
last chapter that magnetism can be generated by elec- 
tricity, and electricity by magnetism ; and that by the 
mechanical movements of the poles of a steel magnet or 
an electromagnet in proximity to the poles of an elec- 
tromagnet, a series of transient electric currents can be 
generated in its coils, flowing alternately in opposite 
directions in such rapid succession as to constitute an 
alternating current. 

Small machines are made on this principle, as illus- 
trated by Fig. 50, in which is shown an electromagnet 
mounted with its poles in proximity to those of a steel 




magnet, and connected with a driving-wheel and 
belt, by which it can be given a rapid rotary mo- 
tion, so that its poles alternately rotate past those of the 
steel magnet, producing an alternate reversal of polarity 



114 



DYNAMOS. 



115 



in its core by which an alternating current is generated 
in its coils. 

By attaching two strips of copper, insulated from each 
other, to its axis, and connecting the terminals of the 
magnet's coils with them as shown, the current may be 
collected by the two copper brushes, A and B, pressing on 
these strips, and transmitted through the external circuit, 
as shown by the arrows. 

If an electromagnet be substituted for the steel magnet 
as shown in Fig. 51, and the terminals of its coils con- 



-< ««. 




nected with the brushes as shown, each magnet 
will generate a current in the coils of the other 
magnet This current is generated by a very small 
quantity of magnetism which is always produced in iron 
by the work done on it in preparing it for use, and is 
called residual magnetism ; hence the current is very 
feeble at first, but as the magnetism is increased in each 
magnet by the current, and the current by the magnet- 
ism, the inductive effect being constantly multiplied in 
this way, the cores quickly become magnetically satu- 
rated, and a powerful current is thus rapidly generated, 
of far greater electric energy than can be generated by 



116 ELECTRICITY FOR EVERYBODY. 

the steel magnet. The cores, after being once magnetized 
in this way, always retain a residnal magnetic charge. 

As the relative positions of the two insulated copper 
strips with which the brushes A and B make contact are 
reversed at each half revolution, at the same instant that 
the transient currents generated in the coils of the re- 
volving magnet are reversed, these currents must all 
pass out in the same direction by one brush and return 
by the other, and therefore circulate in the same direc- 
tion through the external circuit and coils of the station- 
ary magnet, as shown by the arrows. For if a transient 
current passes out by brush B and returns by brush A, 
then, when the strip in contact with B rotates into con- 
tact with A, if the current were not reversed it would 
pass out by A and return by B, but being reversed it 
must pass out by B and return by A as before. Hence 
the alternating current generated in the coils of the re- 
volving magnet is transformed into a direct current in 
the coils of the stationary magnet and in the external 
circuit. 

The revolving magnet is called the armature, because it 
generates the current, and the pair of insulated copper 
strips are called the commutator, because they are the 
means by which the alternating currents are commuted, or 
exchanged for a direct current. 

Large machines constructed on these principles, for 
the generation of electricity, and driven by steam or 
water power, are called dynamos, from a Greek word 
which means power. They are divided into two prin- 
cipal classes, known respectively as direct current dy- 
namos and alternating current dynamos, and, in each 
class, there are many different forms of construction. 
The direct current dynamos are divided into three 



DYNAMOS. 



117 



distinct classes, known respectively as the series wound, 
shunt wound, and compound wound. 

Direct Current Dynamos.— The general construc- 
tion of the direct current dynamo is illustrated by 




Fig. 52. 

Fig. 52, which shows especially the construction of the 
series wound dynamo. The armature consists of a cir- 
cular magnet mounted between two massive pole-pieces 
belonging to the stationary magnet, by which it is partly 



118 ELECTRICITY FOR EVERYBODY. 

inclosed, sufficient space being left on each side for it to 
revolve freely without contact. 

The coils of both magnets being wound in the direc- 
tion shown, when the armature revolves in the direction 
indicated by the curved arrow above, the current flows in 
the direction indicated by the other arrows, producing a 
north pole on the right and a south pole on the left in 
the stationary magnet, in accordance with Ampere's 
rule 5 lines of magnetic force flowing across from the 
north pole to the south, filling the space in which the 
armature revolves, and circulating in two magnetic cur- 
rents through its core on opposite sides, from the lower 
corner of the right pole-piece to the upper corner of the 
left pole-piece. Hence this space is called the magnetic 
field, and the stationary magnet is called the field-magnet. 

The electric current from the field-magnet, after 
traversing the external circuit as shown, enters the 
armature by the lower brush, and divides, like the mag- 
netic current, into two equal currents, which circulate 
through its coils on opposite sides, and leave by the 
upper brush. Hence each half of the armature becomes 
a magnet, as indicated by the circular dotted lines, two 
north poles, marked n n, being produced above, and two 
south poles, marked s s, below, in accordance with 
Ampere's rule. 

On account of this division of the armature current 
between two circuits, the wire used in the armature coils 
of series wound dynamos is much smaller than that used 
in the field-magnet coils, since it carries only half the 
volume of current in each circuit, while the field-magnet 
wire carries the full volume of current in a single circuit. 

The commutator shown has eight copper bars, or seg- 
ments, insulated from each other, the ends of which are 



DYNAMOS. 119 

indicated by the circle of dark spaces, and the armature 
coils are attached to these in such a manner that each 
coil connects two segments, as shown. Hence the field- 
magnet current, entering by a segment through the 
lower brush, and dividing as described, must traverse 
every coil and segment on each side till it reunites and 
leaves by a segment through the upper brush. In like 
manner, the currents generated in the armature coils, 
being added to this current, traverse the coils on each 
side, from the lower to the upper brush. Magnetic lines 
of force are generated in the armature's core by this 
accumulated current, and circulate through it at right 
angles to the electric current. 

The magnetic poles produced by these lines being in 
proximity to the similar poles of the field-magnet, mutual 
repulsion occurs between them, by which the north field- 
magnet pole is pushed downward on the right, and the 
north armature pole upward, the south pole of each 
magnet being deflected in the opposite direction, on the 
left. Hence the poles occupy the positions indicated by 
the letters, as already described. These poles constantly 
maintain these fixed positions, the armature rotating 
through the positions occupied oy its poles. When, there- 
fore, that part of the armature which has north polarity 
rotates downward from the polar position n n to that 
marked ss, the current traversing its coils is reversed as 
it crosses the neutral line on which the brushes are 
placed, and it acquires south polarity; the opposite sec- 
tion of the armature, which had south polarity, having, 
at the same time, rotated upward to the polar position 
n n, and acquired north polarity by a similar reversal of 
the current. 

The current is reversed whenever two opposite com- 



120 ELECTRICITY FOR EVERYBODY. 

mutator segments come into contact with the two 
brushes. In the little armature shown in Fig. 51, which 
has two coils connected with two commutator segments, 
it was shown that a reversal of current occurs at every 
half revolution, and, therefore, two at every full revolu- 
tion ; so that the number of reversals is the same as the 
number of coils, or commutator segments, one occurring 
whenever an opposite pair of segments completes a half 
revolution. Hence the dynamo shown in Fig. 52, having 
eight coils connected with eight commutator segments, 
would have eight current reversals at each revolution, 
and, therefore, eight waves of current traversing its coils 
and external circuit. A dynamo may have forty or more 
coils and commutator segments, and may revolve at the 
rate of 2,000 revolutions a minute, and hence generate 
80,000 or more current waves per minute. 

If the brushes were moved so as to make contact with 
the commutator on a line at right angles to the neutral 
line, the current could neither enter nor leave at the 
polar positions where reversal occurs, consequently a 
current generated in any armature coil as it moved 
through a quarter circle, from a brush to the neutral 
line, on either side, would be neutralized by an equal 
opposite current as this coil moved through the next 
quarter circle, from the neutral line to a brush; so that 
there would be no current to flow in or out through the 
brushes. 

Therefore, when the brushes are moved to any inter- 
mediate position between the neutral line and a line at 
right angles to it, there is a partial neutralization of the 
currents in this way, which varies in proportion to the 
distance of the brushes from the neutral line, increasing as 
they are moved away from it and decreasing as they are 



DYNAMOS. 121 

moved toward it. And in this way, within certain limits, 
the dynamo current is regulated, the brushes being at- 
tached to a yoke having a handle by which they can 
both be moved at the same time, in either direction j their 
movement away from the neutral line being technically 
called giving them lead. 

Series Wound Dynamo. — The dynamo described 
above is called series wound because its field-magnet is 
wound with wire large enough to carry the whole current 
which is transmitted through the armature coils, field- 
magnet coils, and external circuit, in series, as shown. 
Therefore any variation of the resistance encountered 
by the current in the performance of electric work in the 
external circuit, as the production of light or the opera- 
tion of machinery, affects the whole volume of current, 
both in the internal and external circuits, requiring its 
regulation by a movement of the brushes as described, to 
maintain evenness of current. 

Shunt Wound Dynamo. — When a dynamo is so con- 
structed that only a small part of its current is employed 
to magnetize its field-magnet, it is called shunt wound, 
because the magnetizing current is diverted from the 
main circuit through a shunt circuit. This construction 
is illustrated by Fig. 53. The field-magnet is wound 
with fine wire coiled round its core in a great number 
of turns. This wire, on account of its fineness and 
length, has high resistance, so that it carries only a 
small volume of current, ranging from 1J per cent, to 
20 per cent, of the entire volume; but on account of 
the great number of turns in the winding, the electric 
pressure of the current is increased in the same pro- 
portion as its volume is diminished, so that it has high 
magnetizing power. 



122 



ELECTRICITY FOR EVERYBODY. 



The external circuit, which is composed of large wire, 
and has, therefore, comparatively low resistance, carries 
the main current and is entirely independent of the field- 
magnet circuit, and both circuits are connected with the 




Fig. 53. 

brushes as shown. Therefore the current, as it leaves 
the upper brush, divides in proportion to the resistance 
of each circuit, and, after traversing the two circuits, re- 
unites at the lower brush. 



DYNAMOS. 123 

When the current in the external circuit is employed 
for electric work, the electric resistance in this circuit 
being thus increased, the volume of its current is pro- 
portionally diminished j this causes an accumulation of 
electric energy which increases the electric pressure at 
the upper brush, where the current divides, much in the 
same way as an obstruction in a steam or water pipe in- 
creases the steam or water pressure; and as the resistance 
of the field-magnet circuit remains unchanged, a greater 
volume of current is transmitted through it, increasing 
its magnetizing energy, and thus supplying increased 
electric energy for the performance of the work in the 
external circuit. In this way a shunt wound dynamo 
becomes self -regulating within the limits of the magnetic 
saturation of its cores, beyond which its magnetizing 
energy cannot be increased. 

Compound Wound Dynamo. — The series and shunt 
methods of winding may be combined in the same ma- 
chine, producing what is called the compound wound 
dynamo, which is illustrated by Fig. 54. In this dynamo 
there are two separate coils of wire wound on the field- 
magnet core, a coil of fine wire of many turns and a coil 
of coarse wire of fewer turns. The coarse wire coil is 
connected at the brushes with the external circuit, as in 
the series wound dynamo, while the fine wire coil, like 
that of the shunt wound dynamo, is also connected with 
the brushes, but has no connection with the external cir- 
cuit. Both coils are employed to magnetize the field- 
magnet, the coarse wire coil carrying a current of com- 
paratively large volume and low electric pressure, and 
the fine wire coil one of small volume but high electric 
pressure. Hence this dynamo combines the advantage 
of a magnetizing current of large volume in its field- 



124 



ELECTRICITY FOR EVERYBODY. 



magnet circuit, through which the whole current flows as 
in the series wound dynamo, with that of high electric 
pressure in this circuit and of self regulation by the two 
circuits, as in the shunt wound dynamo. By a proper 




Fig. 54. 

adjustment of the relative resistances of the two field- 
magnet coils the best combination for these purposes 
may be obtained. 

Constant Current and Constant Potential. — 
These different dynamos differ in their adaptation to 



DYNAMOS. 



125 



different kinds of electric work. The series wound 
dynamo is found to be best adapted to work which 
requires a current to be maintained constantly at the 
same volume by varying the electric pressure in the same 
proportion as the resistance of the external circuit is 
varied by the quantity of work. Hence it is also called 
the constant current dynamo. But where the work re- 




Fig. 55. 

quires a current to be maintained constantly at the same 
electric pressure, or potential, while the volume of cur- 
rent varies as the resistance produced in the external 
circuit by the quantity of work, the shunt and com- 
pound wound dynamos are found to have the best 
adaptation. Hence they are also called constant potential 
dynamos. 

Armature Construction. — Armatures are constructed 
in different ways, but there are two leading kinds, known 



126 



ELECTRICITY FOR EVERYBODY. 



respectively as the ring armature and the drum or 
cylinder armature. The ring armature, called also, from 
its inventor, the Gramme armature, is shown in Fig. 55. 
It consists of a wide iron ring, round which are wound a 
number of coils of copper wire wrapped with insulating 
material. This ring is attached by bolts to a narrow 
metal ring, without coils, mounted at the rear end with 
spokes on a steel shaft; and on the front end of this shaft 
is mounted the commutator, to whose bars the coils are 
attached by stout connecting wires or rods, as shown. 

The core is 
made up of a 
number of thin, 
flat rings of soft 
sheet-iron, one of 
which is shown 
in Fig. 56, which 
are bound to- 
gether by the 
bolts mentioned* 
above, and insu- 
lated from each 
other with tissue 
paper. This pro- 
duces a lami- 
nated core, 
across which wasteful electric eddy currents cannot cir- 
culate in the iron under the coils, as in a solid core. 

The drum, or cylinder armature, called also, from its 
inventor, the Siemens armature, is shown in Fig. 57. It 
is constructed in the form of a cylinder, and is of greater 
length than the ring armature, and of proportionally less 
diameter. The coils are wound lengthwise on a core 




Fig. 56. 



DYNAMOS. 



127 



mounted directly on the shaft, round which they curve at 
each end, as shown, crossing spirally from one side of the 

cylinder to the other, so that 
there is no interior wire, as in 
the ring armature; and their 
ends are attached to the com- 
mutator, as shown. 

This core is also laminated, 
being composed of sheet-iron 
disks, insulated as above, one 
•of which is shown in Fig. 58. 
In its centre is a hole for the 
shaft, and around this are four 
holes for ventilation, which, be- 
ing placed in line in the several 
disks when the core is con- 
structed, make four ventilating 
tubes which, in some armatures, 
connect with narrow openings, 
at intervals, between the disks. 




Fig. 57. 




Fig. 58. 



In the circumference are projecting teeth, between which, 
when placed in line, are long grooves, in which the coils 
are wound, as shown, and confined either by wooden 



128 ELECTRICITY FOR EVERYBODY. 

wedges above them or by metal bands round the arma- 
ture 5 armatures of this kind being called iron-clad. 

This method of construction is also employed in the 
ring armature, and is called, from its inventor, the Paci- 
notti method. Its principal advantage is that it brings 
the iron of the core close to the pole-pieces of the field- 
magnet, thus reducing the magnetic resistance to its 
lowest practical limit. The lamination is shown at the 
ends of the teeth iu Fig. 57. The core of this armature 
is also constructed with a plain surface, like that shown 
in Fig. 56 ; also without ventilating openings. 

Each of these methods of construction has its special 
advantages. The coils can be more securely confined 
when wound round a ring than when wound on the sur- 
face of a cylinder, and are less liable to displacement by 
centrifugal force. Hence the ring armature can be made 
of any required diameter ; and by giving it large diam- 
eter, its rotary speed can be proportionally reduced 
without reduction of its efficiency. But as the wire in 
its interior and on its ends takes little or no part in 
electric generation, acting merely as a conductor of the 
currents generated in the exterior wire, it increases the 
cost without corresponding increase of efficiency. One 
of the principal advantages of the ring armature is the 
interior ventilation obtained by its open structure, which 
is of the highest importance in preventing the injurious 
accumulation of heat in its coils and core. 

The cylinder armature has the advantage of a more 
compact mechanical structure, and of less wire in propor- 
tion to its efficiency, the only idle wire being that on the 
ends. But its diameter is limited by the difficulty of prop- 
erly securing its coils against displacement in an arma- 
ture of large diameter, especially on a plain surface core ; 



DYNAMOS. 129 

and the accumulation, in such an armature, of a mass of 
comparatively idle end wire confines the heat with over- 
lapping coils, and prevents proper interior ventilation. 
This limitation of its diameter requires higher speed to 
produce the same electric efficiency, the efficiency of an 
armature being largely dependent on the number of lines 
of magnetic force cut by its coils per second or minute. 

Construction op Brushes and Commutator.— The 
brushes are insulated from each other, and are usually 
composed of strips of copper, soldered together at their 
outer ends, and beveled at the ends in contact with the 
commutator. Each brush is usually divided into two or 
more sections, as shown in the dynamo in Fig. 59, which 
are confined in clamps with set-screws, and can be easily 
removed for repairs or replacement. Pressure on the 
commutator is produced by spiral springs, as shown in 
the lower brush ; and by the connecting yoke shown, the 
brushes can be moved to or from the neutral line, for 
regulation of the generating electric pressure, as already 
explained. 

Brushes are also made of solid strips of carbon, which 
are often preferred to copper brushes, as they wear the 
commutator much less and more evenly, leaving its sur- 
face always smooth, and seldom producing sparks at the 
point of contact. 

The beveled point of the brush must be broad enough 
to bridge the space between adjoining commutator bars, 
so as to make contact with the approaching bar, as the 
commutator rotates, before breaking contact with the 
receding bar, thus preventing interruption between the 
successive waves of current, and a spark at each break. 

The commutator is insulated from the shaft, and has 
usually a ventilating space underneath. Its bars are 



130 ELECTRICITY FOR EVERYBODY. 

insulated from each other, usually with mica, and are 
securely bound together by metal collars, insulated from 
them and fitted to beveled shoulders at the ends, and the 
surface is finished in a lathe, so as to be perfectly even 
and smooth. 

Bipolar Dynamo. — The dynamo shown in Fig. 59 is 
called bipolar because it has only two poles, and is corn- 




Fig. 59. 

pound wound, two terminals of the two coils in its field- 
magnet being shown on the left ; the conductors connect- 
ing these coils with the brushes are shown in front, and 
one of the two binding-posts for connecting them with 
the external circuit is shown in the rear ; the other con- 



DYNAMOS. 131 

nections being made underneath. All angular projections 
in the field-magnet core, connecting yoke above, and pole- 
pieces below, are carefully avoided, the corners being 
rounded to prevent magnetic loss by the escape of mag- 
netic lines of force into the air, to which angular corners 
are liable. The joints in these parts are all so closely 
fitted as to be invisible, thus preventing magnetic resis- 
tance from imperfect contacts. The armature is of the 
cylinder type, and the band- wheel, by which its rotation 
is produced, is shown in the rear. 

Field-magnet cores and the parts connected with them 
are usually made of cast-iron, as in this case $ lamination 
being of less importance than in armature cores, and 
cast-iron cheaper than laminated iron. 

Multipolar Dynamos. — Direct current dynamos are 
sometimes constructed with a field-magnet having a cir- 
cular yoke from which a number of poles project inward ; 
the coils being wound on these polar projections in such 
direction as to produce alternate north and south poles all 
around. A dynamo of this kind is called multipolar, and 
may have as many poles as can be conveniently attached 
to its field-magnet yoke. 

In Fig. 60 is shown a four-pole dynamo of this con- 
struction. Its field-magnet coils are wound on bobbins 
fitted to the cores, so that they can easily be removed for 
repairs or replacement; and a pole-piece is attached to 
each core. These four alternate poles produce four al- 
ternate poles in the armature, on two neutral lines 
which cross each other at right angles; and hence four 
brushes are required, one at each polar position in the 
commutator, the two positive brushes being connected 
together, and likewise the two negative. There are there- 
fore twice as manv current reversals at each revolution 



132 



ELECTRICITY FOR EVERYBODY. 



of the armature as in a two-pole dynamo having the same 
number of armature coils, and twice as many waves of 
current traversing the external circuit. Hence, in a 
dynamo of this construction, the rotary speed of the 
armature need be only half that of a two-pole dynamo 




Fig. 60. 



having the same number of armature coils, to produce 
the same number of current waves per minute. In like 
manner any further increase in the number of poles can 
produce a corresponding reduction of armature speed, a 
six-pole dynamo requiring only one third the speed, and 
an eight-pole dynamo only one fourth the speed. And 
as the generation of electric energy depends on the num- 



DYNAMOS. 133 

ber of electric waves produced per minute, as well as on 
the magnetic strength of the field, it is possible, by this 
construction, to reduce the armature's rotary speed, in a 
field of given magnetic strength, without reducing the 
electric energy. But the proportion in which this can 
be done depends on the quantity of power employed to 
rotate the armature against the electromagnetic force, 
and on the general construction of the dynamo. 

In the construction of large dynamos for special elec- 
tric work the multipolar method has the advantage of 
shortening the magnetic circuit between the poles, and 
thus reducing the magnetic resistance, which, in large 
two-pole dynamos, is liable to become excessive, requir- 
ing corresponding increase in the massiveness of the 
cores and connecting yoke for its reduction. But the 
two-pole construction is cheaper and less complicated, 
and hence is generally preferred for small dynamos. 

Alternating Current Dynamos. — A dynamo con- 
structed without a commutator for making the current 
direct in its external circuit, produces an alternating 
current. One of this construction is shown in Fig. 61. 
Two copper rings, mounted on the shaft near the front 
end of the armature, take the place of the commutator. 
These are insulated from each other, and each is con- 
nected with a separate terminal of the armature circuit. 
The current is collected from these rings by two brushes, 
each of which is connected with a separate terminal of 
the external circuit, so that the current-waves, traversing 
this circuit, pass out from one ring and return to the 
other by the brushes, alternately in opposite directions. 

The field-magnet is of the multipolar type, a large 
number of coils, wound in one continuous circuit, being 
attached to a circular yoke, the winding alternately in 



134 ELECTEICITY FOR EVERYBODY. 

opposite directions, so as to produce alternate poles of 
opposite polarity. 

The armature is of the cylinder type, but the coils do 
not cross at the ends, from side to side, as in direct cur- 
rent armatures of this type, but are wound back and 
forth in deep grooves on the face of a laminated core, 
round the projections between the grooves, and held in 
place by wooden wedges above them, making the armature 
ironclad, the iron projecting above the coils. These coils 
are also wound alternately in opposite directions, in one 
continuous circuit, producing alternate poles of opposite 
polarity. 

As the armature revolves, and its poles rotate past 
those of the field-magnet, a current is generated in all 
its coils at the same instant, which follows the winding 
in the same direction. This current is reversed at the 
next instant by the reversal of polarity, as the armature 
poles rotate past the adjacent field-magnet poles, follow- 
ing the winding in the opposite direction, this action 
being sustained continuously by the rotation, with alter- 
nate reversal of the armature current in this manner. 

In large dynamos of this construction, like that shown 
in Fig. 61, the field-magnet is separately excited by a 
small direct current dynamo, called the exciter, which is 
run by a belt from the band- wheel shown on the right, 
while the large dynamo is run by the band- wheel on the 
left. The current from the exciter traverses a set of fine 
wire coils, wound on the field-magnet cores, but does not 
magnetize the field sufficiently for heavy electric work. 
Hence a separate set of coarse wire coils is also wound 
on these cores in the same direction, alternately^ as the 
others, and connected with the armature coils by brushes 
through the commutator shown at the right of the two 



136 ELECTRICITY FOR EVERYBODY. 

collecting rings, by which part of the armature current 
is made direct for the purpose of magnetizing the field. 
Increase of electric resistance in the external circuit, 
caused by the increase of electric work, produces a pro- 
portional increase in the volume of this magnetizing 
current, and decrease of resistance, a corresponding de- 
crease in the volume of current, in the manner explained 
on page 123, thus making this dynamo self -regulating 
within the limits of the magnetic saturation of its cores, 
as in direct current shunt and compound wound dynamos. 
This magnetizing current can be varied by the movement 
of the brushes on the commutator, as in direct current 
dynamos, producing corresponding variation in the pres- 
sure and volume of the main current. 

Transformers. — The electric pressure at which the 
alternating current is generated by large dynamos ranges 
usually from 1000 to 5000 volts. This pressure is much 
higher than necessary for ordinary electric work, but is 
capable of transmitting a current through a compara- 
tively small copper wire, having high electric resistance, 
to a distance of several miles with but little loss, thus 
effecting a great saving in the cost of copper wire in a 
long external circuit. The current transmitted at this 
high pressure can be reduced to a current of low pres- 
sure, with corresponding increase of volume, at the place 
where it is required for use. This is accomplished by an 
instrument called a transformer, which is practically an 
induction-coil of special construction, as illustrated by 
Fig. 62. 

Like the induction-coil, it has an iron core and two 
coils of copper wire, a primary and a secondary,- which 
are insulated from each other and from the core in 
the most thorough manner. The core, instead of being 



DYNAMOS. 



137 



inclosed within the coils, partly incloses them, and is 
composed of a number of sheet-iron plates insulated 
from each other with tissue paper, forming a laminated 
structure like that of an armature core, which is bolted 
together in an iron frame, as shown. This construction 
brings the core equally close to both coils, as shown in 




Fig. 62. 



the cross-section in Fig. 63, so that both are equally ex- 
posed to its magnetic inductive influence, instead of the 
secondary coil being separated from it by the primary, 
and hence receiving only a minor share of that influence, 
as in induction-coils. 

The fine wire coil is usually made the primary and 
connected with the dynamo circuit, while the coarse wire 
coil becomes the secondary, and is connected with the 



138 



ELECTRICITY FOR EVERYBODY. 



lamp or motor circuit where the work is to be done. 
Hence the electric transformation is usually the reverse 
of that in the induction-coil, being from high to low elec- 
tric pressure, with corresponding increase of current 
volume, instead of from low to high pressure with cor- 
responding decrease of current volume. Thus a dynamo 
current of a 1000 volts pressure may be transformed into 
an electric lighting current of 50 volts pressure and 





V 



Fig. 63. 

twenty times the volume, adapted to the supply of a 
large number of incandescent lamps or small motors. 
Such a current can be employed in a building with per- 
fect safety, while a 1000- volt current would be dangerous. 
Where this current is transmitted to a distance of sev- 
eral miles at a high pressure, it is received at the station 
by a large transformer, which is divided into several 
sections, each of which bears its proportional part in the 
transformation; each one of ten sections, for instance, 
performing a tenth part of the work. From this station 
it is distributed to the buildings in a large district, at 
each of which it passes through a small transformer, and 



DYNAMOS. 139 

its pressure is again reduced. Thus a current of 4000 
volts may be reduced in the large transformer to 400 
volts, and in each small transformer to 50 volts. 

The transformer may be employed for increasing in- 
stead of diminishing the electric pressure, by reversing 
the usual connection of its coils with the dynamo and 
circuit. Thus a low-pressure current may be transformed 
into a high-pressure current, at the generating station, 
for the purpose of long distance transmission, and be 
transformed oppositely to a low-pressure current, at the 
receiving station. A 54-volt current has, in this way, 
been transformed into a 30,000- volt current, transmitted 
more than 100 miles, and then reduced to a 100-volt 
current, with a total loss of only 28 per cent, of efficiency. 



CHAPTER VI. 

Electeic Motoes. 

Principles of Construction. — It has been shown 
that the dynamo is a machine for the transformation of 
the mechanical energy produced by steam or water-power 
into electric energy ; and that this energy can be con- 
veyed by wires to any point where it is required for use. 
One of the principal uses to which it is applied, when 
generated in this way, is the operation of machinery 5 
and in order to apply it to this use, it must be trans- 
formed back again into mechanical energy by the ma- 
chine known as the electric motor. 

The general construction of these motors is, in all re- 
spects, the same as that of dynamos. They have the 
same principal parts, the armature, field-magnet, commu- 
tator or collecting rings, and brushes 5 and are classified 
in the same way, as direct current and alternating cur- 
rent; and the direct current as series wound, shunt 
wound, compound wound, bipolar, and multipolar. A 
motor can be employed as a dynamo and a dynamo as a 
motor, and the same general principles of construction 
apply to each. 

Where a motor is connected with the electric circuit, of 
a dynamo, as shown in Fig. 64, and the armature of the 
dynamo is rotated by mechanical power in opposition to 
the electromagnetic force, an electric current is gene- 
rated, which traverses the motor and causes its armature 

140 



ELECTRIC MOTORS. 



141 



to rotate in obedience to the electromagnetic force, re- 
producing the mechanical power, which can be applied to 
the operation of any kind of machinery. Hence the two 
machines, connected in this way, become a convenient 
apparatus for the electric transformation of power, and 
its distribution and application. 




Dynamo. 



Fig. 64. 



Motor. 



Counter Electric Pressure. — But the rotation of the 
motor's armature, in this way, generates electric pressure, 
the same as if it were rotated by mechanical power, and 
this pressure opposes that of the dynamo. Hence, if both 
machines were of the same size, this counter pressure 
would nearly neutralize that of the dynamo when the 
motor's speed nearly equaled that of the dynamo, as 
would be the case if the motor were doing no work. But 
when it is applied to work, its speed being reduced, this 
counter pressure is correspondingly reduced, and a pro- 
portionally stronger current supplied by the dynamo for 
the performance of the work. This pressure thus be- 
comes a means of automatic regulation of the current, so 
as to make it proportional to the work. 



142 ELECTRICITY FOR EVERYBODY. 

Hence, if the speed of the dynamo be increased in the 
same proportion as the work required of the motor, the 
necessary speed for the performance of the work will be 
maintained by the motor. And as increase of speed by 
the dynamo requires increase of power, it is evident that 
the power applied to the dynamo must always vary as the 
work required of the motor. 

Relative Size of Dynamos and Motors. — While the 
general principles of construction are the same in the 
motor as in the dynamo, there are certain specific differ- 
ences which adapt each machine to its specific use. The 
motor, being intended for the distribution and application 
of the power transformed into electricity by the dynamo, 
is usually a much smaller machine. A dynamo of 100 
horse-power, for instance, may be employed to operate 
100 motors of approximately one horse-power each, or 
twenty motors of approximately five horse-power each, 
or any other number within the limits of its power ; the 
dynamo being located at the source of power, the steam- 
engine or water-wheel, while the motors are distributed 
to the various points where power is required for use. 

Electric Distribution of Power.— Thus power may 
be distributed by a dynamo and motors from a steam- 
engine in the basement to the various departments of 
industry on the upper floors of a large building, for the 
operation of lathes, saws, stamping presses, paper cutters, 
printing presses, and other machinery, cheaper and more 
conveniently than it would be possible to distribute the 
power direct from the engine by belts and shafting. 
And the electric energy may also be employed for light- 
ing and heating the building. In like manner, the power 
employed in a large factory, covering perhaps several 
acres, may be more economically distributed by wires 
than by belts. 



ELECTRIC MOTORS. 143 

But one of the chief advantages of this system is in its 
distribution of power from a central station, in or near a 
town or city, where it can he generated on a large scale 
by steam or water, and supplied to customers at much 
cheaper rates than they could generate it themselves. 
Such stations are also employed to generate and distrib- 
ute electric energy for lighting and heating, as well as 
power, thus keeping the machinery in constant operation, 
and the capital invested constantly employed. 

Various small industries can thus be supplied with 
power where the use of a steam-engine would be imprac- 
tical, inconvenient, or prohibitive. The motor occupies 
but little room, requires but little care, and furnishes 
power at a moment's notice, by the simple turning of a 
switch, without the delay, labor, heat, dirt, and annoy- 
ance of the small steam-engine, with its furnace and 
boiler, requiring a proper outlet for its steam and smoke, 
continual attention, to supply fuel and water and remove 
ashes and cinders, and frequent repairs, and the constant 
menace of danger from incompetent management. 

Instances have come under the writer's notice where 
motors have been in constant daily use for years, without 
costing a cent for repairs, or requiring any care or atten- 
tion, except for starting and stopping, and renewing the 
supply of oil, once a day, in self -oiling bearings. These 
motors were of three to five horse-power, and took the 
place of gas-engines of the same horse-power, whose use, 
for some years previous, had been a constant source of 
annoyance and expense, requiring continual watching; 
while that of the motors, at nearly the same cost for 
current as had been paid for gas, was entirely satisfactory. 

The electric system of power transmission is especially 
adapted to mines, in which its superiority to the pneu- 



144 ELECTRICITY FOR EVERYBODY. 

matic system of power transmission by compressed air, 
formerly in extensive use, has been amply demonstrated 
both in the cost of installation and subsequent mainte- 
nance in proper repair, in its superior efficiency for the 
operation of the various apparatus and the running of 
the tram cars, and in the cheapness and facility with 
which it can be changed from one part of the mine to 
another, as old diggings are abandoned and new ones 
opened. 

Niagara Falls Electric Power Stations. — The 
great water falls at Niagara have been estimated to be 
capable of developing over seven million horse-power. 
There are at present in operation or in course of construc- 
tion four principal electric power stations having an 
aggregate capacity of over 500,000 horse-power. The 
earliest of these, the plant of the Niagara Falls Power 
Co., is situated on the American side of the falls and is 
now operating at its full capacity of 105,000 horse-power. 
The water for this station is taken from the Niagara 
River about a mile and a half above the falls and is con- 
veyed by means of a short surface canal to the two 
power houses of the plant situated on each side of the 
canal. There are in all 21 vertical turbines in the wheel 
pits of this plant about 200 feet below the surface, and 
the water is delivered to these turbines through vertical 
steel penstocks each iy 2 feet in diameter. After 
passing through the turbines the water discharges 
through a tunnel 7,000 feet long into the Niagara River 
a few hundred feet below the falls. These 21 turbines 
drive 21 alternating current dynamos placed on the sur- 
face over the turbines and connected to them by means 
of long vertical shafts. Each dynamo has a capacity of 
5,000 horse-power, and generates two phase alternating 



ELECTRIC MOTORS. 145 

currents at 2,200 volts. This is transformed to three phase 
currents at 22,000 volts by means of step-up trans- 
formers, and is transmitted at this high pressure to 
Buffalo and to intermediate points. 

The other three large electric power stations are situ- 
ated on the Canadian side of the Niagara River, namely, 
that of the Canadian Niagara Power Co., of the Toronto 
and Niagara Power Co., and of the Ontario Power Co. 

The hydraulic arrangements of the Canadian Niagara 
Power Co.'s station are similar to those of the Niagara 
Falls Power Co. The Canadian power house is situated 
in the Queen Victoria Niagara Falls Park, about half a 
mile above the Horseshoe Falls. The water is taken from 
the river through a short canal, delivered through steel 
penstocks to the turbines at the bottom of the wheel pit, 
and discharged through a tunnel about 2,000 feet long 
into the river below the falls. There will be eleven 
turbines installed, each driving an alternator on the sur- 
face by means of a long vertical shaft. Each of the 
eleven alternators will have a capacity of 10,000 horse- 
power, and will generate three phase alternating currents 
at 11,000 volts, making an ultimate capacity of 110,000 
horse-power. At present four units have been installed. 

The power house of the Toronto and Niagara Falls 
Power Co. is in course of construction on the bank of 
the Niagara River about a mile above the Horseshoe 
Falls. Its arrangements of turbines and dynamos will 
be in general similar to those of the two plants already 
described. The discharge water will be carried away by 
two tunnels, one from each end of the wheel pit, which 
two tunnels will come together and form the main dis- 
charge tunnel which passes under the Niagara River and 
discharges at the base of the Horseshoe Falls at a point 

10 



146 ELECTRICITY FOR EVERYBODY. 

about midway between the American and Canadian 
banks. This power house will contain eleven turbines 
and generators with a total capacity of 125,000 horse- 
power. At present three units have been installed. 

The power house of the Ontario Power Co. is situated 
on the Canadian bank of the lower Niagara River, directly 
below the Horseshoe Falls. This power house differs 
radically in its construction from those already de- 
scribed. The water is taken from the upper Niagara 
River at the head of the Dufferin Islands, over a mile 
above the falls, and is carried through a steel pipe, — laid 
directly beneath the surface of the ground, — to the power 
house, where it passes through steel penstocks to the tur- 
bines and then discharges directly into the river. The 
turbines are of the horizontal type and each turbine is di- 
rectly coupled to an alternator having a capacity of 12,500 
horse-power and generating three phase alternating cur- 
rents at 12,000 volts. The ultimate capacity of this 
station will be 180,000 horse-power. Three units have at 
present been installed. A unique feature of the electrical 
equipment is the installation of all switching and con- 
trolling apparatus in a separate transformer house on the 
bluff above the power house instead of directly in the 
power house. 

Loss of Power in Electric Transmission. — Whenever 
power is transmitted over a distance there is an inherent loss 
of power in the transmission wires. The amount of the 
loss depends upon the distance of transmission, and upon 
the size and kind of wires employed. This loss can be kept 
as low as desired, and is determined in practice by the 
first cost of the transmission line and by the cost of gen- 
erating the electric power. This loss is generally less 
than in power transmission by mechanical means. 



ELECTRIC MOTORS. 147 

This is especially true of long distance electric trans- 
mission for the running of street cars, as compared with 
cable transmission for the same purpose ; the greater 
proportion of the power, in the latter case, being con- 
sumed in moving the heavy cable, and overcoming the 
friction of the supporting pulleys, leaving, on the aver- 
age, a smaller proportion for moving the cars ; whereas, 
in the electric system, much the larger proportion is 
employed in moving the cars. 

Stationary Motors. — Motors employed for station- 
ary work, in shops, factories, and elsewhere, are nearly 
all of the direct current kind, and may be either series, 
shunt, or compound wound. When required for steady 
work, in which the variation of strain is not excessive, 
and automatic regulation of the first importance, so that 
the motor shall require little or no attention, except to 
start and stop it and supply it with oil, the shunt wound 
motor is generally preferred; the relative supply of cur- 
rent in the two circuits of a well-constructed machine of 
this kind varying automatically in proportion to the 
work, in the same manner as in the shunt wound dy- 
namo, without danger of overheating and injuring the 
coils. 

Where the variation of strain is excessive, as in the 
operation of elevators and dock hoists and the blowing of 
large pipe organs, special automatic regulation is re- 
quired, and compound wound motors are sometimes pre- 
ferred for such work. 

Rheostats. — The rheostat is an apparatus for admit- 
ting the current to the motor gradually, so as not to heat 
and injure the coils and insulating material by admitting 
the full current before the armature has attained its full 
rotary speed, and developed corresponding counter elec- 



148 



ELECTRICITY FOR EVERYBODY. 



trie pressure; electric energy producing heat when ex- 
cessive, and not fully employed for mechanical work. 
The rheostat is also employed for regulating the volume 
of current, to adapt it to the requirements of the work. 
Its general construction is shown in Fig. 65. A num- 
ber of coils of German-silver wire, which has very high 
electric resistance, are connected together in series and 
inclosed in a box. This series of coils is connected with 
a circular row of brass stops on the lid of the box ; one 
or more coils being connected with each stop, except the 
neutral coil on the left. A brass switch has a rotary 
movement over these stops ; one end of it resting on a 
main circular stop, while the other end rests on one of the 

smaller stops. 
One terminal of 
the electric cir- 
cuit is connected 
with the main 
stop, and the 
other terminal 
with the series 
of coils by the 
right-handsmall 
stop. Therefore, 
when the switch 
is moved from 
the neutral stop 
on the left to 
Fi s- 65 - the first stop 

connected with the series of coils, the current, entering 
from the dynamo by the main stop, must traverse the 
switch and all the coils, encountering their full resistance, 
before it can leave for the motor by the right-hand stop. 




ELECTRIC MOTORS. 149 

But as the switch is moved to the right, from stop to 
stop, this resistance is gradually cut out, till the right- 
hand stop is reached, when it is all cut out, and the cur- 
rent flows direct to the motor. 

This construction is varied to adapt it to different 
classes of motors and different kinds of work, and to the 
separate circuits of field-magnet and armature. The 
rheostat may be employed merely to start the motor, or 
also to regulate the current, or to reverse its direction in 
armature and field-magnet. For such work as the blow- 
ing of pipe organs, or the operation of elevators, the 
switch is often moved automatically in opposite direc- 
tions alternately, over the stops, and the supply of current 
thus adjusted to the requirements of the work; increas- 
ing as the electric resistance in the rheostat decreases, 
and decreasing as this resistance increases. 

Reversal of Rotation. — Reversal of rotation is re- 
quired in many kinds of work, as in the upward and 
downward movements of an elevator or dock hoist, or the 
backward and forward movements of a street car. This 
is sometimes accomplished by a mechanical device, as a 
belt-shifter, or a clutch ; but it is often preferable to re- 
verse the rotation of the motor's armature, which can be 
done by reversing the direction of the current, either 
in the armature or the field-magnet, but usually in the 
armature. This reversal of current reverses the relative 
polarity of the armature and field-magnet, so that the 
magnetic attraction and repulsion, by which rotation in 
a given direction is produced, are reversed, producing 
rotation in the opposite direction. But if the direction 
of the current were reversed in both armature and field- 
magnet, the relative polarity would remain unchanged, 
and therefore the rotation would not be reversed. 



150 ELECTRICITY FOR EVERYBODY. 

The reversal is sometimes accomplished by two sets of 
brushes attached to the same conductors, but placed in 
reversed positions on the commutator; one set being 
lifted out of contact as the other set is depressed into 
contact ; so that the current which, for instance, entered 
the commutator below and left above, by the first set, 
enters above and leaves below by the other set, and there- 
fore traverses the armature coils in the opposite direc- 
tion. The same result may be accomplished by one set 
of brushes, and a rheostat with two sets of stops, so con- 
nected with the circuits of the field-magnet and arma- 
ture that the direction of the armature current may 
be reversed by reversing the movement of the switch, 
while the field-magnet current remains unreversed. 

Alternating Current Motors. — The construction of 
alternating current motors varies greatly, and is much 
more complicated than that of direct current motors. 
The general construction, in its simplest form, is similar 
to that of alternating current dynamos, and consists 
of a circular, multipolar field-magnet, inclosing a cylinder 
armature with coils wound back and forth in grooves on 
its face. These coils have no connection with either the 
field-magnet coils or external circuit, but form a closed 
circuit within themselves, without any external outlet, 
the terminals being soldered together. 

The cores of both field-magnet and armature are lami- 
nated; and the field coils are wound in two series, on 
alternate poles, as shown in Fig. 66, so as to produce 
north and south polarity alternately, in each series, all 
around the field; eight field coils being shown, four in 
each series, and four armature coils, the ends of which 
are shown. But these relative numbers may vary in 
different motors. 



ELECTRIC MOTORS. 



151 



The current from the dynamo traverses each series of 
field coils alternately, reversal of current occurring after 
every two successive waves. A current wave entering at 
B, traverses the series connected with that terminal, and 
returns to the dynamo by A. The next current wave, 




Fig. 66. 



entering by G, without reversal, traverses the series con- 
nected with that terminal, and returns also by A. The 
current is then reversed at the dynamo, and the next 
two successive waves enter by A ; the first turning to the 
right, traversing the series connected with C and return- 
ing by that terminal ; and the second turning to the left, 



152 ELECTRICITY FOR EVERYBODY. 

traversing the series connected with B, and returning by 
that terminal. 

Alternate field poles of opposite polarity being pro- 
duced in this way by each current wave induce, in the 
armature, alternate poles of opposite polarity to the 
adjacent field poles and to each other. And as each 
successive current wave magnetizes a series of field poles 
a step in advance of those magnetized by the receding 
wave, the armature is rotated round, step by step, by the 
magnetic attraction and repulsion between its poles and 
those of the field-magnet ; the field polarity thus travel- 
ing round the stationary field, and forcing the rotary 
armature to follow it. 

This action may be better understood by considering 
its effect on a single armature pole. Suppose a north 
pole is induced in the armature by a south pole in the 
field-magnet 5 the next current wave produces a south 
field pole adjacent to this armature pole, on one side, 
which attracts it, and a north field pole adjacent to it, on 
the other side, which repels it in the same direction ; and 
the armature is rotated a step by these two forces. The 
next wave produces the same effect, and the armature 
is rotated round another step. And thus it continues to 
rotate, step by step, till it has made a complete revolution, 
and is ready to make another in a similar manner. The 
same action having occurred at every pole, the rotary 
force is multiplied proportionally. And as the waves 
follow each other with great rapidity, the speed of 
rotation is proportionally rapid. 

It is evident that the distance to which an armature is 
rotated by each current wave depends on the number of 
poles in the surrounding field-magnet. With an eight- 
pole field-magnet, for instance, each armature pole is 



ELECTRIC MOTORS. 153 

rotated through one eighth part of the circumference, or 
twice as far as with a sixteen-pole field-magnet. Hence, 
with a given number of current waves per minute, the 
speed of rotation varies inversely as the number of field 
poles, as in direct current machines. 

Two Phase Motors. — Motors constructed to operate 
with two sets of field coils, receiving from the dynamo 
two distinct waves of current, following each other suc- 
cessively in this way, and each appearing in the field 
circuit a certain number of degrees in advance of its pre- 
decessor, as described above, are called two phase motors, 
and are the kind now in most general use, especially for 
heavy work. Special construction is required in the 
dynamos by which such motors are operated, and also in 
the circuit which connects the two machines ; this circuit 
requiring a double construction, with three parallel 
wires ; each outside wire carrying a current wave alter- 
nately, to or from each set of coils, which returns by the 
central wire, as described above; and the armature of the 
dynamo requiring to be wound in two circuits, to supply 
these alternate waves. 

Single Phase Motors. — Motors designed to be oper- 
ated on a two wire circuit by alternating current dynamos 
of the ordinary construction are called single phase motors. 
Their construction has not been so fully developed as 
that of the two phase motors, but the importance of 
adapting alternating current motors to the two wire cir- 
cuits and alternating current dynamos already in use for 
electric lighting has stimulated invention, and brought 
into market, recently, several different motors of this 
class, especially those designed for light work; though 
such motors are also constructed for heavy work. 

These motors are usually constructed with two sets of 



154 ELECTRICITY FOR EVERYBODY. 

coils, in which the two different phases of current appear 
alternately at different points, as in two phase motors. 
But these alternate phases, instead of being produced by 
a special construction in the dynamo, and transmitted by 
a double circuit, as described above, are produced by a 
special construction in the motor itself, which varies 
greatly in different motors. 

The successful operation of an alternating current 
motor requires that the alternations of current and the 
reversals of polarity should occur at the same instant in 
both field-magnet and armature, and also that there 
should be synchronism between the action of the motor 
and the dynamo from which it receives its current. But 
such motors are liable to a momentary lag in the in- 
ductive effect of the field-magnet on the armature ; and 
also to the generation of an opposing electric pressure in 
the armature coils by self-induction, which partly neutra- 
lizes the currents induced by the field-magnet. 

Both these effects interfere seriously with the operation 
of the motor, especially in starting, before it has attained 
full speed ; and the efforts of inventors have been directed 
to various means of suppressing them, which have proved 
successful to such a degree, that very efficient alternating 
current motors are now in practical use, more especially 
those of the two phase kind. 

Among the most important improvements has been the 
application of tinfoil condensers, for the suppression of 
self-induction, like those employed on telegraph lines; 
also a double construction in both field-magnet and arma- 
ture; as if two motors of the same construction were 
joined together, end to end, in such a manner that the 
field poles in one come opposite the spaces between field 
poles in the other, so that the action of each alternately 



ELECTRIC MOTORS. 



155 



supplements that of the other, as the coils in each sepa- 
rate field are traversed alternately by a reversed wave of 
current. 

Railway Motors. — Motors for railway service require 
a very different construction from those designed for 
stationary work. On account of their exposed position 




Fig. 67 

under the cars, an iron or steel armor, water-tight up to 
the axle, has been found necessary, and is easily provided 
by employing, for this purpose, the connecting yoke to 
which the core projections of a bipolar or multipolar 
field-magnet are attached, as shown in Fig. 67. This 
armor is about three-quarters of an inch thick, and fur- 
nishes ample protection against water, mud, dirt, and 
obstructions liable to be met with on the track. It is 
ventilated either above or at the sides, and constructed 



156 ELECTRICITY FOR EVERYBODY. 

with upper and lower sections, which can be raised or 
lowered on a hinge, as shown, for the removal of the 
armature when repairs are required. 

Reduction of speed is another very important matter. 
This was accomplished at first by two sets of gears, by 
which the high speed of the armature was reduced to the 
low speed required for the car axle. The production of 
high speed, and its subsequent double reduction in this 
way, was not only a wasteful process, resulting in the 
useless consumption of energy, but the noise occasioned 
by so much gearing, and by the friction of the brushes on 
a high-speed commutator, was very objectionable to the 
passengers. 

Reduction of the armature's speed without reduction of 
the motor's efficiency was evidently the proper remedy ; 
and this has been accomplished in three ways : either by 
increasing the diameter of the armature, so that it shall cut 
the same number of lines of magnetic force per minute, 
at slower speed; or by increasing the number of field- 
magnet poles, so as to produce the same number of cur- 
rent waves in the circuit, per minute, at slower speed, as 
already explained; or by a combination of both these 
methods. 

In one of these three ways, according to the preference 
of the inventor, motors have been constructed in which 
only K)ne set of gears is required to produce the same 
rate of speed as formerly required two sets. These are 
known as single reduction motors, and have taken the 
place of the old double reduction motors on most street 
railways. The prevention of useless waste of energy and 
wear of the machinery, with corresponding reduction in 
cost of maintenance and increase of comfort for pas- 
sengers by the suppression of noise, are their most prom- 



ELECTRIC MOTORS. 157 

inent features. The motor shown in Fig. 67 is of this 
construction. 

A further reduction of armature speed, in the manner 
indicated above, has resulted in dispensing entirely with 
gearing, producing the gearless motor, in which the 
speed of the armature is reduced to the requirements 
of the car axle 5 the armature being mounted either 
directly on the axle, or on a hollow shaft inclosing it, and 
connected with it in such a manner as to allow indepen- 
dent spring pressure. To bring the speed within the 
requisite limits, with this construction, requires a motor 
with an armature of much larger diameter than that of 
the single reduction motor, and a field-magnet of corre- 
sponding size, occupying more space under the car, and 
hence requiring greater elevation of the car above the 
track. Such motors are evidently better adapted to ele- 
vated roads and tunnel roads, where high speed is per- 
missible, and size and massiveness not objectionable, 
than to surface roads. They are in successful operation 
on such roads, at a speed of 12 to 26 miles an hour, and 
also on some surface roads, at a speed of 10 to 20 miles 
an hour. 

All railway motors now in use are of the direct current 
kind, and are series wound; and the wire used in the 
coils of both armature and field-magnet is much larger 
than in stationary motors of similar winding, so as to be 
capable of carrying a current of much greater volume. 
The wire in the field coils is much larger than in the 
armature coils, as in all series wound machines, since it 
carries the full current, while the armature current is 
divided between the two circuits on opposite sides of 
the armature. 

This current being under constant manual control, 



158 ELECTRICITY FOR EVERYBODY. 

automatic regulation, like that employed in stationary- 
motors, with shunt or compound winding, is not only 
unnecessary, but would be impracticable under the exist- 
ing conditions ; these motors being subject to excessive 
variations of electric strain far beyond the range of such 
automatic regulation. A car may be running nearly 
empty, on the level, on one part of its route, requiring 
barely enough current to keep it in motion at the proper 
speed ; and, on another part, may be loaded to its utmost 
capacity, and require sufficient current to start it after 
stoppage, and move it up a steep grade. 

This supply of current is regulated by a rheostat under 
control of the motor-man, and can be increased or dimin- 
ished as required, by the movement of the controller 
switch; the large wire composing the motor's coils being 
capable of carrying sufficient current to supply power for 
any emergency, without danger of injury to the coils by 
overheating. 

Electric Railways. — The usual construction of elec- 
tric railways is illustrated by Fig. 68. There is a central 
station where the power is generated, usually by steam, 
and transformed by dynamos into electricity, which is 
transmitted to the motors under the cars by an electric 
circuit composed usually of the rails for one branch, and 
of a bare copper wire suspended above the track, for 
the other branch. This wire is attached to insulators, 
supported either on cross wires, as shown in the cut, or 
on brackets, by poles of wood or iron, and the rails are 
connected together at the ends, for this purpose, by bonds 
of heavy copper wire, as shown, making the circuit con- 
tinuous ; and the rails on opposite sides of the track are 
also connected by similar cross-wires, to equalize the 
current on both sides. 



ELECTRIC MOTORS. 



159 



Two motors are 
usually employed 
on each car, and 
connection be- 
tween them and 
the rails is made 
through the car- 
wheels and axles, 
and between them 
and the line wire, 
by a wire connect- 
ed with a wheel 
called the trolley, 
which is carried 
at the end of 
a pole supported 
on the car roof 
by springs which 
press the trolley 
upward against 
the line wire; the 
construction be- 
ing such as to al- 
low the pole a hor- 
izontal motion for 
rounding curves 
in the line, or re- 
versing its posi- 
tion. 

The line wire is 
divided into sec- 
tions, each of 
which carries suf- 




Fig. 68. 



160 ELECTRICITY FOE EVERYBODY. 

ficient current to run the cars on that section, and re- 
ceives its supply through a feeder wire, which forms 
part of the circuit and is connected with the dyna- 
mos at the station. These feeder wires are wrapped 
with insulating material, and form cables which are 
supported on the poles parallel with the line wire, as 
shown. 

There may be half a dozen or more cars running on 
the same section at the same time, each tapping the line 
wire by its trolley, and taking so much current as it re- 
quires, and all thus taking current in parallel ; the supply 
of current in this way being similar to the supply of 
water or gas to buildings along a street, by service pipes 
tapping the main pipe at various points. 

The current may be transmitted from the positive poles 
of the dynamos, either through the feeder wires and line 
wire, returning to the negative poles by the rails, as 
shown by the arrows ; or through the rails, returning by 
the line wire and feeder wires ; the practice being now 
adopted of reversing the direction of the current through 
the circuit at stated intervals, to prevent injury to water 
and gas pipes adjacent to the track by the electrolysis 
caused by a current constantly flowing in the same 
direction. 

The cars can be lighted and heated more economically 
and satisfactorily by the current which supplies the power 
than in any other way j part of it being diverted through 
electric lamps and heaters for this purpose. 

On elevated roads, and tunnel roads, the current is 
often supplied by a third rail, and the circuit completed, 
either by another such rail on a parallel track, or by the 
track rails as above described. Conductors, either of 
copper or iron, may also be laid in conduits adjacent to 



ELECTRIC MOTORS. 161 

the track, for the same purpose, in cities where overhead 
wires are not permitted ; but this system is much more 
expensive than the overhead system, and it is difficult to 
insulate bare conductors properly in conduits ; but it has, 
nevertheless, been successfully accomplished. 

Running Cars by Storage Batteries. — Various at- 
tempts have been made to run cars by storage batteries, 
carried on the cars, and charged at a central station when 
exhausted j relays of charged batteries taking the place 
of those exhausted. But this system, from which so 
much was once expected, has not proved successful in 
practice, and has usually been abandoned after trial. 
The great weight of the battery, 3,600 pounds to a car, 
has always been a serious objection; but the failure to 
produce batteries of the requisite durability and efficiency 
for such work, has been the most serious defect in this 
system. 

Lightning Arresters. — The electric apparatus con- 
nected with an air line for an electric railway or any 
other electric purpose requires special protection against 
lightning, which is furnished by the apparatus known as 
the lightning arrester, of which there are many different 
kinds, all constructed on the same general principle. The 
line wire passes through a box, in which it is connected 
with two rows of sharp points, one row on each side of a 
short bend in the wire, between which is another row 
connected with a wire leading direct to the earth. 

The dynamo current, no matter how strong its pres- 
sure, will follow the bend; but the enormous electric 
pressure of a lightning discharge on the line, causes the 
current produced by it to leap across the narrow air 
space between one of the rows of points connected with 
the line and the central row, and pass to the earth by the 
11 



162 ELECTEICITY FOR EVERYBODY. 

ground wire ; so that it is arrested in its course before it 
can reach the dynamos, motors, or other apparatus. 

These arresters are placed at intervals all along the line, 
and also in the station and on the cars; and afford a 
limited protection, but not always sufficient to prevent 
injury to the apparatus, which, during severe thunder- 
storms, often receives a sufficient electric charge to burn, 
or seriously damage, the coils of dynamos or motors, or 
injure other apparatus in a similar manner. 

Recording Watt-Meter. — Meters for the separate 
measurement of electric pressure and current volume 
have already been described; but as both pressure and 
volume are elements of the electric current, it is evident 
that a meter designed to measure current sold to con- 
sumers for the supply of motors, lamps, or heaters, should 
include both elements. This has been accomplished by a 
meter invented by Elihu Thomson, shown in Fig. 69 ? 
which records the full electric energy of the current in 
watts ; the watt being an electric unit obtained by mul- 
tiplying the volt, which represents pressure, into the 
ampere, which represents volume. 

It consists mainly of an electric motor constructed 
without iron cores, either in its armature or field. Two 
field coils wound with coarse wire are arranged to be 
connected with the electric circuit in series, so as to carry 
the whole volume of current. These coils inclose an 
armature mounted on a vertical shaft, as shown, wound 
with fine wire, which forms a shunt circuit between the 
two wires of the main circuit, and carries a current of 
very small volume, which nevertheless represents the full 
electric pressure by which both branches of the current 
are impelled. Hence current volume, represented in the 
field coils, combined with current pressure, represented 



ELECTRIC MOTORS. 



163 



in the armature coils, produces rotation of the armature, 
which puts in motion a train of clock-work, contained in 
a case above, by which the electric energy, supplied to a 
consumer, is recorded on dials, graduated on a decimal 




Fig. 69. 

scale, in the same manner as gas consumption is recorded 
in a gas meter. 

This record is made in watt-liours ; a current of one 
watt, that is of one ampere with a pressure of one volt, 
flowing for one hour, recording one watt-hour. Hence 
a current of 500 watts, that is of five amperes with a 
pressure of 100 volts, or of ten amperes with a pressure 
of 50 volts, would record 500 watt-hours, in one hour, 
1,000 watt-hours in two hours, and so on. 



164 ELECTRICITY FOR EVERYBODY. 

At the lower part of the meter is shown a disk, made of 
copper or aluminum, attached to the armature shaft, and 
three permanent steel horseshoe magnets with their poles 
brought close together, and arranged so that the disk ro- 
tates between these poles. By this means the eddy cur- 
rents induced in the disk produce a retarding force which 
is directly proportional to the speed, and this speed is 
thus made directly proportional to the electric energy 
passing through the meter. 

The Single Phase Alternating Current Railway 
Motor. — A direct current series motor will turn in the 
same direction irrespective of the direction in which the 
current passes through the motor. A series motor will, 
therefore, operate with alternating current. The solid 
field magnets of a direct current series motor would, how- 
ever, have strong eddy currents induced in them by the 
alternating currents and these would produce excessive 
heating; there would also be vicious sparking at the 
commutator owing to the self-induction of the armature. 

The single phase alternating current railway motor 
which has recently been introduced is a series motor in 
which the entire magnetic circuit of the field magnet is 
built up of sheet steel punchings so as to minimize these 
eddy currents ; these steel punchings are held together in 
a steel frame forming a box type of motor similar in its 
outer appearance to a direct current railway motor. The 
alternating current motor has also a neutralizing field 
winding in addition to the regular field winding in order 
to counteract the self-induction of the armature and so 
reduce sparking. The armature is practically the same 
in the alternating and direct current motors. 



CHAPTER VII. 

Electric Lighting. 

Heat and Light by Electric Resistance. — The 
transmission of electricity through any substance always 
generates a certain quantity of heat, which varies in pro- 
portion to the electric resistance of the substance. If the 
substance is a good electric conductor, like copper, and 
large enough to carry the current easily, the heat may 
be barely perceptible ; but if it is a bad conductor, like 
platinum, carbon, or air, the heat may be sufficient to 
produce combustion or incandescence, especially if the 
conductor is too small to carry the current easily. And 
it is by means of apparatus constructed on this principle 
that electric light and heat are produced. 

There are two systems of electric lighting in common 
use, known respectively as arc lighting and incandescent 
lighting; arc lighting being the older, and having at- 
tained considerable prominence before the incandescent 
system came into use. 

Arc Lighting. — In the general construction of the 
various lamps now in common use for arc lighting, two 
carbon rods are employed, which are made from some 
good carbon, as petroleum coke, ground fine and made 
into a paste with gas-house pitch, or some similar hydro- 
carbon, and then molded and baked with a great deal 
of care; going through various processes to give them 
the requisite purity, density, hardness, straightness, and 
electric resistance. 

165 



166 



ELECTRICITY FOR EVERYBODY. 



">1^ 



Fig. 70. 



They are supported vertically 
in the lamp, one above the other, 
as shown in Fig. 70. The upper 
one is about twelve inches long, 
and the lower one, which is con- 
sumed only half as fast, is about 
six inches long; each being about 
seven-sixteenths to one-half an 
inch in diameter. The electric cur- 
rent is transmitted through them 
downward, from the upper to the 
lower carbon, and its action in pro- 
ducing the light is controlled and 
regulated by the apparatus con- 
tained in the brass case in the 
upper part of the lamp, above 
which connection is made with the 
electric circuit; and the light is 
produced between the points of 
the two carbons, when separated 
for this purpose, as shown at 
A in Fig. 71. 

This apparatus is constructed 
with a brass rod to which the up- 
per carbon is attached by a set 
screw. This rod passes through 
a loose washer connected by a 
clutch with a laminated iron ar- 
mature, which has a free vertical 
movement between the poles of 
an electromagnet, the coils of 
which are connected with the 
electric circuit. The current 



ELECTRIC LIGHTING. 



167 



when admitted by the switch shown above in Fig. 70, tra- 
verses these coils, passes thence through the brass rod 
and the two carbons, and returns to the dynamo by the 
wire on the left, as shown by the arrows. When this 
occurs the ar- 
mature is at- 
tracted upward 
from the posi- 
tion shown at 
B to that shown 
at A; the clutch 
tilting the loose 
washer, so that 
it grips the 
brass rod, lift- 
ing it, and sep- 
arating the car- 
bons about one 
eighth of an 
inch, as shown. 
The carbons 
become hot at 
the points, but 
their electric 
resistance is 
not sufficient 
to make them 

hot enough to produce light till separated 
count of the greater resistance of the air, the light bursts 
out in the air space between them ; the points becoming 
incandescent, and the air space filled with burning car- 
bon vapor from their combustion, producing a light of 
about 1,500 to 2,000 average candle-power. The con- 





Fig. 71. 



when, on ac- 



168 ELECTEICITY FOR EVERYBODY. 

sumption of the carbon keeps both rods pointed, and a 
little pit, called the crater, forms in the npper point, as 
shown, from which the light is radiated downward. 

The flame takes the form of an arc, from which the 
name arc light is derived. This is caused chiefly by the 
difference of potential between the burning vapor and 
external air, producing electric attraction outward, and 
equality of potential between the molecules of the vapor 
within the air space, producing electric self-repulsion 
outward ; the center of the flame curving outward while 
its tips adhere to the points above and below. The up- 
per tip circulates round the edge of the crater as the car- 
bon burns away ; and as the force is greatest toward the 
side from which this tip starts, the outward curve is 
always on that side. 

There is a shunt circuit of fine wire, not shown, which 
is wound on the cores of the electromagnet in the op- 
posite direction to that of the main circuit, so that a cur- 
rent passing through it tends to reverse the polarity 
produced by the main current, and hence correspond- 
ingly weakens the magnetism. This circuit branches off 
from the main circuit above the magnet and reunites 
with it below the magnet, without including the carbons. 

As the carbons burn away the distance between them 
increases, producing corresponding increase of electric 
resistance in the air-space. This reduces proportionally 
the volume of current in the main circuit, and increases 
that in the shunt circuit, and in both ways weakens the 
magnetism ; and when it becomes so weak that the weight 
of the armature and connected rods can no longer be sus- 
tained, they drop down, and the edge of the washer 
strikes the little post, supported on a fixed disk, by which 
the washer is tilted back into the position shown at B, so 



ELECTRIC LIGHTING. 



169 



that it loosens its grip on the brass rod, which slips down 
through it, bringing the carbons closer together. This 
renews the volume of current in the main circuit, and the 
magnetism, so quick that the descent of the upper carbon 
is stopped when the distance between the carbons is suf- 
ficiently reduced; and the constancy of the light is thus 
automatically regulated. This method of regulation is 
so sensitive, that the apparatus responds instantly to very 
slight variations of resistance in the arc. 




If the lamp is accidentally extinguished, the supply of 
current in the main circuit being thus interrupted, the 
magnetic action is so weakened that the upper carbon 
drops into contact with the lower one, renewing the main 
current and magnetism instantly and relighting the lamp. 

The loose washer method, which has been used for il- 
lustration on account of its simplicity, has been super- 
seded in practice by the clutch shown in Fig. 72, which is 
more certain in its action and less liable to obstruction. 
By comparing G and J) in Fig. 72, with A and B in Fig. 



170 



ELECTRICITY FOE EVERYBODY. 



Fig. 73. 



71, it will be seen that the action 
of the clutch is practically the 
same as that of the washer. 

Double Carbon Lamp. — One 
pair of carbons will last for six or 
eight hours ; but when light is re- 
quired for a longer period without 
renewal of carbons, a lamp with 
two pairs, like that shown in Fig. 
73, is required, in which a double 
clutch is employed, by which one 
pair are kept separated till the 
other pair are consumed. This is 
accomplished simply by so con- 
structing the double clutch that it 
lifts the upper carbon of the 
second pair a little higher than 
that of the first pair ; so that when 
the first pair are in contact there 
is space between the second pair. 
But when the first pair are con- 
sumed, the current being inter- 
rupted, the second pair instantly 
come into contact, and the light is 
renewed ; such a lamp furnishing 
light for twelve or sixteen hours 
without renewal of carbons. 

The arc light requires a power- 
ful current, usually of ten amperes, 
with a pressure of 1,500 to 2,500 
volts, supplying 25 to 50 . lamps 
connected together in series, the 
current flowing from lamp to lamp. 



ELECTRIC LIGHTING. 171 

Hence each lamp must be so constructed that its supply 
of current shall not in any way interfere with the supply 
of current to the others ; otherwise the accidental extin- 
guishing of one lamp, by the consumption or breaking 
of its carbons, would stop the flow of current, and thus 
extinguish all the lamps in the circuit; or any varia- 
tion of resistance in a lamp would, by causing a varia- 
tion in its supply of current, affect the brilliancy of 
the light in all the others; so that, in a circuit of 25 
or 50 lamps, there would be a continual flickering of 
the light by this variation of resistance in different 
lamps. 

Cut-Out. — The method of regulation already de- 
scribed keeps the light steady, but does not provide 
against interruption of the current by the accidental 
breaking of the carbons, or their entire consumption 
in a lamp; which requires a cut-out by which the full 
current can flow through a separate channel, inde- 
pendent of the carbons, and also of the magnet coils. 
This consists of a short horizontal brass bar, attached to 
a lever connected with the clutch which separates the 
carbons. This bar makes contact with two binding-posts 
connected with the main circuit, when the lever is de- 
pressed, but when the clutch lifts the upper carbon, it 
also raises this lever, and withdraws the cut-out bar from 
its contact with the posts, so that the main current, which 
flowed through the bar, must now flow through the car- 
bons. But the instant a lamp is extinguished, so that the 
magnetism ceases, this lever drops, and pushes the cut-out 
bar against the posts, so that the current flows through it 
to the other lamps. 

But as current would still flow through the shunt cir- 
cuit, which, from its increased strength, might heat and 



172 ELECTRICITY FOR EVERYBODY. 

injure the fine wire magnet coil connected with it, and 
also create sufficient magnetic attraction to retard the fall 
of the cut-out lever, an auxiliary electromagnet is pro- 
vided, wound oppositely with two sets of coils, like the 
principal magnet, through which the shunt current is 
diverted, for a moment, till the current through the cut- 
out bar is fully established, cutting out the magnet coils. 

There are also resistance coils and other minor auxil- 
iary apparatus, which regulate the supply of current and 
movement of the carbons, but need not be described. 
This construction also varies considerably in the different 
kinds of lamps, but its main principles are essentially the 
same in all. 

Enclosed Arc Lamps. — In the arc lamps just described, 
the carbons burn away rapidly because they are heated to 
incandescence in the presence of an excess of air, and 
must be replaced after about six or eight hours. In an 
enclosed arc lamp a small glass globe is used to enclose 
the lower carbon and a portion of the upper carbon, 
which latter passes loosely through a gas valve in the 
upper part of the glass globe. Free access of air is 
thereby prevented from reaching the incandescent carbon 
tips, and the combustion of carbon is, therefore, much 
slower, so that a pair of ordinary carbons last about one 
hundred hours in the enclosed lamp. 

Flaming Arc Lamps. — In the ordinary carbon arc 
lamps the light is given out from the incandescent carbon 
tips, while the arc itself gives but little light. Recently 
several new types of arc lamps have been placed upon 
the market, in which the arc is made luminous so as to 
be the principal source of light; these have for this 
reason been called flaming arc lamps. 

In one type of flaming arc lamp special or mineralized 



ELECTRIC LIGHTING. 173 

carbons are used. These mineralized carbons contain, in 
mixture or as a core, some salt of a metal as calcium or 
titanium, which is evaporated by the heat of the arc 
and renders this highly luminous. The light given by 
these lamps is of a reddish-yellow or a white color. 

A second type of flaming arc lamp is the magnetite lamp, 
in which metallic copper and magnetite are the electrodes. 
The magnetite or black oxide of iron used in this lamp is 
mixed with a salt of titanium and compressed in powdered 
form into a thin iron tube forming a stick about the size 
of an ordinary arc lamp carbon and which forms the nega- 
tive electrode. The copper electrode is the upper and 
positive electrode. The magnetite lamp can only be used 
on direct current. The magnetite is slowly consumed, 
lasting from one hundred to two hundred hours. The 
copper remains unchanged and does not have to be re- 
newed. The magnetite lamp gives a strong white light, 
which is essentially the spectrum of titanium. 

Flaming arc lamps have the advantage over ordinary 
carbon arc lamps of giving several times the amount of 
light for a given expenditure of electrical energy. 

Incandescent Lamps. — The ordinary incandescent 
lamp consists of a thin piece of carbon about the size of 
a horse hair and about six inches long, called a filament, 
which is enclosed in a pear-shaped glass globe, from 
which the air has been exhausted by means of specially 
constructed air pumps so as to produce a nearly per- 
fect vacuum. 

These carbon filaments were originally made by carbon- 
izing strips of substances such as bamboo, cellulose, bass- 
broom cotton, linen and silk. At present these filaments 
are made by squirting a viscous preparation of carbon 
through dies, and then baking, shaping and treating these 



174 ELECTRICITY FOR EVERYBODY. 

threads of carbon so as to bring them up to the constitu- 
ency required for the incandescent lamp. The ends of 
the filament are attached to fine platinum wires which are 
melted through a glass stopper, which is then melted into 
the bottom of the glass globe. Platinum wires are used 
to bring the terminals out through the glass, because the 
coefficient of expansion of platinum is the same as that 
for glass. The outer ends of the platinum wires are con- 
nected to the lamp terminals by copper wires. 

The electric current in passing through this carbon fila- 
ment heats it to incandescence and it thus becomes a 
source of light. The exclusion of air from the filament 
prevents its combustion. The effect of the continued 
heating is, however, to slowly deteriorate the filament, 
owing to the presence of traces of air, and to other causes, 
so that the light given out by an incandescent lamp 
diminishes gradually with use. For this reason these 
lamps are not used until the filament is actually destroyed, 
but it is usual to replace them after they have burnt from 
600 to 1,000 hours, after which the light given out is so 
reduced as to make them uneconomical to operate. The 
efficiency of incandescent lamps varies from 3.1 to 3.5 
watts per horizontal candle-power when the lamps are 
new. 

Recently incandescent lamps with metallic filaments, 
instead of the usual carbon filaments, have been placed 
upon the market, notably in Europe. The tantalum and 
tungsten lamps are the most prominent examples of these 
metallic filament lamps. While these metals have long 
been known, it is only very recently that means for work- 
ing them have been developed by which thin threads such 
as are needed for lamp filaments can be commercially 
made. These metallic filaments can be operated at a 



ELECTEIC LIGHTING. 175 

higher degree of incandescence than carbon filaments 
and for this reason these metallic filament lamps have a 
much higher efficiency, which varies from 1.15 to 2 watts 
per horizontal candle-power. 

The Nernst Lamp. — In the Nernst lamp there is in- 
stead of a long thin filament of carbon or metal, one or 
more short filaments, each about ■£% inch in diameter and 1 
inch long, made of the oxides of the rare metals mixed 
with suitable binding materials. These filaments, or 
gloivers as they have been termed, are non-conductors of 
electricity when cold, but become conductors when 
heated to a red or white heat. In this lamp means must, 
therefore, be provided to heat the glowers when starting 
the lamp. This is accomplished in the commercial lamp 
by heaters which consist of thin platinum wires wound 
upon thin hollow cylinders of porcelain. These platinum 
wire heaters are connected in shunt with the glowers. 
When current is turned on the lamp it passes through 
the heaters, but cannot pass through the glowers because 
these are cold and do not conduct. The platinum heaters 
are heated to a white heat by the current and this heat 
radiates to the nearby glowers, bringing them to a red 
heat in from 15 to 30 seconds. The glowers now become 
conductors and current passes through them and heats 
them to a white heat and these now give out a powerful 
white light. As soon as the current passes through the 
glowers it also passes through the electromagnet of a 
cut-out, which disconnects the heaters from the circuit. 
The heated glowers have the property of diminishing in 
resistance with increase in temperature; if such 
glowers were connected directly across a constant poten- 
tial circuit the current would, therefore, keep on increas- 
ing until the glowers would burn out. To prevent this 



176 



ELECTRICITY FOR EVERYBODY. 



it is necessary to connect a steadying resistance in series 
with the glowers, which resistance must be made of a 
material which increases in resistance with increase in 
temperature and, therefore, with increase in current. A 
thin iron wire, enclosed in a small glass globe exhausted 



Line 




Glower b *rt LE tt*co. jH .y. 

Fig. 74. 

of air,- is used in the Nernst lamp for this purpose, and 
this iron wire resistance has been termed a ballast. The 
connections of the elements in the Nernst lamp are shown 
in Fig. 74. The glowers in the Nernst lamp are enclosed 
in a glass globe to protect them from draughts and to 
keep in the heat, but this globe is not exhausted of air, 
but has on the contrary free access of air. 



ELECTRIC LIGHTING. 177 

The Mercury Vapor Lamp. — In the mercury vapor 
lamp a column of mercury vapor, enclosed in a glass tube, 
is rendered incandescent by passing an electric current 
through the vapor. The standard 110 volt mercury 
vapor lamp, manufactured by the Cooper Hewitt Electric 
Co., consists of a glass tube, 1 inch in diameter and 45 
inches long, which has been exhausted of air. At the 
lower end of this tube is a small bulb containing about 
one pound of metallic mercury, which forms the negative 
electrode of the lamp. At the other end of the tube is a 
pear-shaped enlargement called a condensing chamber. 
The positive electrode of the lamp, consisting of a short 
cylinder of iron or graphite, is supported in the centre of 
the tube near the upper end. Connection to the elec- 
trodes is made by means of platinum leading-in wires. 
Owing to the presence of the mercury in the otherwise 
exhausted tube this is always filled with mercury vapor. 
If the two electrodes of the lamp are connected to a 110 
volt direct current circuit, the mercury electrode being 
connected to the negative side, and the iron or graphite 
electrode to the positive side, no current will pass through 
the lamp. The reason for this lies in the fact that there 
is an extremely high resistance between the negative elec- 
trode and the mercury vapor. If the current is once 
started this high negative electrode resistance disappears 
and the current continues to flow through the lamp. If 
the current is interrupted, however, for even the shortest 
time, this high negative electrode resistance reasserts itself. 
Means must, therefore, be provided in the mercury vapor 
lamp for breaking down the negative electrode resistance 
on starting the lamp. This is most conveniently done by 
tilting the lamp until the mercury bridges across the tube 
from the negative to the positive electrode, thus forming 

12 



178 ELECTRICITY FOR EVERYBODY. 

a metallic circuit through the mercury ; wheu this bridge 
of mercury breaks, an arc follows which breaks down the 
negative electrode resistance, and the current then con- 
tinues to flow through the mercury vapor. The heated 
mercury vapor also has the property of diminishing in 
resistance with increase in temperature, so that a balanc- 
ing resistance must be used in series with the lamp. The 
standard lamp takes a current of 3.5 amperes. In the 
operation of the lamp, the negative electrode is disinte- 
grated, forming mercury vapor ; this condenses again in 
the upper part of the tube, and the condensed mercury 
flows back, thus reconstructing the negative electrode. It 
is for this reason that a substance like mercury must be 
used for the negative electrode. The positive electrode 
undergoes no change in the operation of the lamp. The 
lamp as described here can only be used on direct current. 
A special form of mercury vapor lamp has recently been 
designed which operates on alternating current. 

Parallel System of Electric Distribution. — Elec- 
tric current is generally distributed for incandescent light- 
ing by the parallel system, already referred to in connec- 
tion with stationary motors and electric railways. In this 
system the lamps are placed on short parallel circuits be- 
tween supply wires which branch off from the main wires 
as shown in Fig. 75, so that each lamp receives the sup- 
ply voltage, and takes the current it requires independent 
of all the other lamps. 

The amount of current taken by any lamp is deter- 
mined by the resistance of its filament j for an ordinary 
100 volt 16 candle-power incandescent lamp this current 
is one half ampere. The total amount of current which 
must be supplied to a group of incandescent lamps is 
equal to the number of lamps multiplied by the current 



ELECTRIC LIGHTING. 



179 



taken by one lamp. For instance, if there are 2,000 
lamps in a circuit, each of 100 volts and 16 candle-power, 
the current supplied will be 1,000 amperes, while the 
voltage supplied is 100, just the same as when only one 
lamp is in circuit. 



QID 



*<!>*** 



T3. 



m 




Street 



Mains 



+ 



a 



Fig. 75. 



When current for incandescent lighting is supplied 
from street mains, the latter are tapped by feeder wires 
opposite each building as shown in Fig. 75. Only so much 
current flows into each building as is required by the 
lamps in circuit. Each feeder circuit is led to a con- 
venient point in the building from which separate cir- 
cuits are led off, each supplying a group of lamps. In 
large buildings there may, however, be a number of such 



180 ELECTKICITY FOR EVERYBODY. 

centres of distribution from which the individual branch 
circuits are supplied. Each of the branch circuits has a 
switch for opening and closing the circuit. Short pieces 
of an easily fusible metal of high resistance, such as tin 
or lead, called fuses, are also connected in each branch 
circuit. The object of these fuses is that they should 
melt and interrupt the circuit, in case the current be- 
comes excessive, due to accident, and so prevent the wires 
from becoming overheated and possibly starting a fire. 
The fuses are placed in a fire-proof box so that they do 
not produce a fire hazard when they melt. There are 
also fuses and a switch in the main circuit at its entrance 
in the building. 

When current for incandescent lighting is supplied from 
a central station all the dynamos are usually connected to 
two heavy copper bars, called Ms bars, by which the 
dynamos are all connected in parallel, and from which 
all the incandescent lighting circuits are supplied. 

Three-Wire System. — In the Edison three-wire system 
of distribution, the dynamos at the station are coupled 
together in pairs, the positive pole of one dynamo and 
the negative pole of the other being connected with the 
same bus bar, called the neutral his, and the two remain- 
ing poles being each connected with a separate bus bar. 
Each supply circuit has three wires which are connected 
to these three bus bars, and extend through the streets, 
and are tapped by similar circuits extending into the 
buildings, in which the lamps are placed on short wires 
which connect the central wire with either outside wire, 
as shown in Fig. 76, and making two parallel circuits 
supplied by three wires instead of by four wires as would 
be required by two circuits in the two-wire system ; 
there is thus a saving of one wire, a very material item 



ELECTRIC LIGHTING. 



181 



in the expense of the large copper wires required in the 
parallel system. 






<k 



^TTT 



Mm 



>SfreeZ .Mai?is 



- 




yC 


© 


/ 


§ 


/ 


8 


> 


I 




s 




s 


S k 


s 


x 


J3» 


Vi 


^ 


+ 





Fig. 76. 



The two outside wires carry the principal part of the 
current for both circuits, which flows through the lamps 
from the positive to the negative wire. But when more 
lamps are lighted in one circuit than in the other, as is 
usually the case, more current, proportionally, is required 
by the circuit having the greater number lighted. The 
neutral wire carries, therefore, only the excess of the cur- 
rent in one outside wire over that in the other outside 
wire. The neutral wire can, therefore, be made of smaller 
cross-section than the outside wires. 



CHAPTER VIM. 
Heat and Electricity. 

Electric Heating. — The use of electricity for heating 
is comparatively recent, and has been made practical, 
within certain limits, by the invention of properly con- 
structed heaters. But the cost of current is still a serious 
obstacle to its general use, so that, notwithstanding its 
superior advantages, it cannot compete successfully with 
other means of heating till current can be supplied more 
cheaply than at present. 

But on electric railways, where all the facilities for 
supply of current are already in use, so that the additional 
current required for heating the cars can be had by a 
little enlargement of the generating apparatus, it has 
been found that heat can be supplied in this way more 
economically than by any other method j about 35 cents 
a day, per car, being the average cost. 

Dewey Heater. — Among the electric heaters which 
have come into successful practical use is the Dewey 
heater, employed both for car heating and for house and 
office heating. It is constructed with an iron case having 
openings above and below for the free circulation of the 
air, as shown in Fig. 77. This case incloses one or more 
coils of wire, made of a composite metal which has high 
electric resistance, and therefore becomes hot when the 
coil is traversed by the electric current. Each coil is 
wound in a great number of turns, separated by narrow 

182 



HEAT AND ELECTRICITY. 



183 




air spaces, on two porcelain insulators, which are notched 
to keep the wire in place, and supported on a vertical 
iron plate in the center of the case, extending from end 
to end; one insulator resting on the upper edge of 
the plate and 
the other on its 
lower edge; the 
plate being per- 
forated with 
holes for air 
circulation. 

The two ter- 
minals of the 
coil are con- 
nected with the 
electric circuit 

at the points of Fig. 77. 

attachment shown at the upper corners, and in the two- 
coil heaters shown, one or both coils may be employed, 
according to the degree of heat required ; the two being 
either placed side by side, as shown in the lower heater, 
or one above the other, as shown in the upper heater. 
Single-coil heaters, like the upper half of the upper 
heater, are also made for attachment to the side of a 
car, or wall of a room. 

These heaters may be employed advantageously in the 
house or office, to furnish a mild heat in chilly weather, 
when the furnace is not in use, or to heat bed-rooms and 
other small apartments ; or they may be employed ex- 
clusively instead of other heating apparatus, to furnish 
any degree of heat required, by those who can afford to 
pay for sufficient current. 

Fig. 78 shows a street-railway car equipped with four 



184 



ELECTRICITY FOR EVERYBODY. 



single-coil heaters, which are sufficient to heat a small 
car, six being usually employed for large cars ; the object 
being to distribute the heat evenly in different parts of 




Fig. 78. 

the car by several single-coil heaters, instead of concen- 
trating it at one or two points by a smaller number of 
two-coil heaters. They fit easily under the seats, as 



HEAT AND ELECTRICITY. 185 

shown, and may be attached either to the floor or sides 
of the car. 

They are connected with the electric circuit in different 
ways, and the current is admitted by the closing of a 
switch, or excluded by opening it. They may be con- 
nected in a single series, in which all the heaters are in- 
cluded ; or in two series connected together in parallel, 
in each of which half the heaters are included ; or in two 
separate series, each connected with the circuit by a sepa- 
rate switch, so that, when both switches are closed, all the 
heaters are in use, but when only one is closed, half of 
them are in use ; the connections being so arranged, in 
the latter case, that the heaters in use are on opposite 
sides of the car. 

By these different methods the heat can be adapted to 
the requirements of the climate and season ; the parallel- 
series method giving the strongest heat, and the heat 
produced by each of the other methods being propor- 
tioned to the number of heaters in use. 

The incandescent electric lamps by which the car is 
lighted are also shown in Fig. 78, making the electric 
equipment complete, for heating, lighting, and propulsion. 

Carpenter Heater. — In the Carpenter heater the coils 
are imbedded in a special insulating enamel, on iron 
plates made in any convenient form, either flat or cylin- 
dric, and inclosed in iron cases of any suitable style, 
which may resemble ordinary heating stoves, and are 
furnished with openings for radiation of the heat, and 
for ventilation. 

Advantages of Electric Heatlng. — The great con- 
venience of the electric system of heating over every 
other system becomes apparent when we consider that it 
furnishes heat without dirt, dust, smoke, or smell, supply- 



186 ELECTRICITY FOR EVERYBODY. 

ing it instantly when wanted by the simple closing of a 
switch, or excluding it instantly when not wanted by the 
opening of the switch, so that there is no waste of cur- 
rent: while heating by stoves, furnaces, steam, or hot 
water involves the labor and expense of supplying coal, 
making and caring for the fire, removing ashes and cin- 
ders, with attendant dirt, dust, and smoke; or of main- 
taining a supply of water in the boiler, and keeping 
boiler, pipes, and coils in repair; there being always a 
considerable waste of heat, even under the most favor- 
able conditions. The electric system includes all the 
advantages of every other system without any of the dis- 
advantages; even dispensing with chimneys and smoke- 
stack. Hence whenever current can be furnished at such 
cost as to make its use economical, electric heating must 
come into general use, wherever current is obtainable. 

Electric Cooking. — Electricity can be employed more 
economically for cooking than for space heating, because 
the heat can be concentrated under each cooking utensil 
separately, so that none is wasted on the surrounding 
air ; and far less current is required in proportion to the 
work accomplished than in space heating. Hence, even 
at the present cost. of current, this method of cooking can 
be employed economically wherever current is obtainable. 

The electric cooking range is far superior, in conven- 
ience and comfort, to the coal or wood range, and fully 
equal to the gas range. The cost of current is no greater 
than that of gas, as usually supplied, and the heating of 
the kitchen, in summer, still less than that of gas ; while 
there can be no such thing as an explosion in the oven, 
or danger incurred by the escape of gas, to which even 
the best gas range is liable by careless use ; the electric 
range being absolutely free from every element of 
danger. 



HEAT AND ELECTRICITY 



187 




Cooking utensils are prepared for electric use by the 
Carpenter method, by attaching to the bottom of each an 
iron plate, as in the 
electric tea-pot shown 
in Fig. 79, which is 
coated with the spe- 
cial enamel already re- 
ferred to, in which is im- 
bedded a coil of com- 
posite metal wire, the 
same kind as that used 
in the heaters; the 
plate being supplied 
with a socket by which 
the coil can be con- 
nected with the electric 
circuit. 

The wire in this coil is 
corrugated, as shown in 
Fig. 80, to prevent the 
enamel from being cracked 
by expansion and contrac- 
tion of the coil, in heating 
and cooling ; the difference 
of expansion by heat, be- 
tween the enamel and this 
wire, being too slight, in 
these short corrugations, 
to produce injury. 

The range consists sim- 
ply of a slab of marble or 
slate, on which the various utensils are placed, as shown 
in Fig. 81. Above this is a switch-board, to the back of 



Fig. 79. 




Fig. 80. 



188 



ELECTRICITY FOE EVERYBODY. 



which are attached a number of spring- jacks, connected 
with the electric circuit; and by thrusting a plug into 
one of these spring-jacks, through a hole in the board, 




Fie. 81. 



any utensil can be connected with the circuit . by its 
socket, through a flexible conductor attached to this plug, 
as shown. 



HEAT AND ELECTRICITY. 



189 




On the right is shown the oven, constructed with coil- 
bearing plates for heating above and below ; the connec- 
tions of which with the electric circuit are so arranged 
that by the turning of a switch the heat can be regulated 
for any kind of work, so as to produce a strong heat or a 
mild heat, as may be required. Water tanks can also be 
arranged with suitable connections, either for a constant 
supply of hot water or for laundry work. 

Electric Ironing.— In Fig. 82 are shown four laundry 
irons, with flexible conductors attached, by which con- 
stant connection with the 
electric circuit, and hence a 
steady heat, can be maintained 
while the iron is in use; so 
that the same iron can be used 
continuously ; the heating by 
the electric current being 
equalized by the cooling by 
evaporation from the damp 
clothes. Thus one iron can 
do the same work as several 
by the ordinary process, and 
the changing of irons and 
caring for the fire, the scorch- 
ing and soiling of the clothes, 
and the heating of the kitchen 
or laundry in warm weather 
are avoided. 

Electric Welding. — Met- 
als can be welded more perfectly by electric heat than by 
furnace heat, and the electric process is now employed 
successfully, not only for welding together metals capable 
of being united by the ordinary process, but also for 



CJ, 




Fig. 82. 



190 ELECTRICITY FOR EVERYBODY. 

welding which is impracticable by this process. This in- 
cludes the welding of such metals as cast-iron and cast- 
steel, copper, brass, tin, lead, bismuth, bronze, and Ger- 
man silver ; each of which can not only be welded to its 
own kind, but to any other kind of metal. 

The process consists simply in pressing the two pieces 
of metal together while heated at the junction by an elec- 
tric current till they become soft enough to unite. Two 
bars, for instance, may be pressed end to end and fused 
together, in this way, instead of being lapped, and ham- 
mered or rolled together, as by the ordinary process. 
The experiment is easily performed with two or three 
storage battery cells ; but, for practical work, a welder of 
special construction is required. This machine is made 
with massive copper clamps for gripping and holding the 
metals, applying the pressure, and admitting the current 
close to the junction. The alternating current is usually 
preferred, and is supplied by a dynamo specially designed 
for the purpose, at a high electric pressure, which is re- 
duced in the welder, by a transformer of special construc- 
tion, to low pressure, with corresponding increase of vol- 
ume, which may be varied as required for different kinds 
of work. 

Wire cables can be successfully welded by this process, 
also metal tubes, and it can be advantageously employed 
for repairing broken shafts and other parts of massive 
machinery. It can also be used with special advantage 
for welding joints in electric conductors; a welded joint 
having the same conductivity as any other part of the 
conductor, and being free from the electric resistance 
and liability to oxidation of joints made by contact and 
soldering. The time required for making a weld varies 
according to its kind, from a second to three minutes. 



HEAT AND ELECTRICITY. 191 

Electricity Generated by Heat. — Electricity can be 
generated by beat, as well as beat by electricity. This is 
accomplished by an instrument called the thermopile, 
which is constructed with a number of short bars of two 
different kinds of metal which show a great difference 
of electric potential under the influence of heat. Bis- 
muth and antimony are the metals usually selected for 
this purpose. An equal number of bars of each metal, 
about six inches in length, are arranged in a series 
in which the bars of each metal alternate with each 
other, and are either soldered or electrically welded 
together, end to end, at the junctions 5 being arranged in 
a compact pile, with insulating spaces between, so that 
alternate junctions are at opposite ends of the pile. 

By 'mounting this pile on an insulating support and 
exposing one end of it to heat, alternate junctions are 
heated, and a current of electricity generated, which 
flows from the bismuth to the antimony bars through the 
heated junctions, and from the antimony to the bismuth 
bars through the alternate junctions at the opposite end 
of the pile, and hence continuously in the same direction; 
the circuit being completed by a copper wire, or other 
conductor, attached to the terminal bismuth bar at one 
end of the series, and the terminal antimony bar at the 
other end. The electric generation may be greatly in- 
creased by cooling one end of the pile while heating the 
opposite end, so that while the junctions at one end are 
heated, the junctions alternating with them, at the other 
end, are cooled; thus producing a difference of electric 
potential proportionate to the difference of heat potential. 

This is a very sensitive instrument, being capable of 
generating a perceptible electric current by an imper- 
ceptible degree of heat ; hence it is employed as a ther- 



192 ELECTRICITY FOR EVERYBODY. 

mometer in delicate laboratory experiments with heat ; 
but it cannot be used for generating electricity for ordi- 
nary practical use; the electric current generated by it 
being weak, and the degree of heat which may be applied 
without fusing the bismuth, very limited. Various at- 
tempts have been made to construct powerful electric 
batteries on this principle ; metals being employed which 
do not fuse easily, and a high degree of heat applied; 
but no permanent practical success has resulted from 
these experiments. 

The earth itself is doubtless a great thermopile, gen- 
erating electric currents by the difference of potential 
between its heated and cooled parts, as explained in 
Chapter II. 

Various attempts have also been made to produce 
electromagnetic motors which can be operated by the 
direct application of furnace heat, without the interven- 
tion of the steam engine and dynamo ; but no practical 
results have yet been accomplished in this way, though 
laboratory experiments have demonstrated the possibility 
of constructing motors of this kind having very limited 
energy. 



CHAPTER IX. 

The Telegkaph and Telephone. 

Simple Telegraph Equipment. — The electric tele- 
graph, in its simplest form, consists of an electric circuit 
connecting the points between which telegraphic inter- 
course is established, a battery at each point, connected 
with this circuit, and two instruments, one for transmit- 
ting and the other for receiving electric impulses by 




Line 



Earth\ 



-gey T 



TOW 

5s 



Sounder 



^l! 



11 

Battery, 



3 



\Earth\ 



Fig. 83. 



which arbitrary signs representing written language are 
produced. 

As batteries have already been fully described in 
Chapter III, it is only necessary to remark that the 
gravity battery, there described, is the one in general use 
for telegraphing in America, as it is not liable to polari- 



13 



193 



194 



ELECTRICITY FOR EVERYBODY. 



zation, has great constancy, and needs but little care. 
But in large offices, in the principal cities, the dynamo is 
now generally employed instead of the battery. 

The circuit is constructed either with a zinc-coated 
iron wire or hard-drawn copper wire supported on poles 
by glass insulators, and connected, through two of the 
instruments, with the positive pole of one battery and 
the negative pole of the other, as shown in Fig. 83 j the 
remaining pole of each battery being connected, through 
the remaining instruments, by a short wire, with the 
earth, by which the circuit is completed. The earth, in 
this case, is not considered a conductor in the same 
sense as the wire, but as an electric reservoir, from which 
electricity is obtained at one end of the line, and to 
which an equal quantity is restored at the other end. 




Fig. 84. 



The Key. — The transmitting instrument is called a 
key, and is constructed as shown in Fig. 84, with a 



THE TELEGRAPH AND TELEPHONE. 



191 



hinged lever which can be depressed by an insulating 
knob in opposition to a supporting spring, so as to bring 
into contact two points, shown under the lever on the 
left, and thus close the circuit ; one terminal of the cir- 
cuit being connected, through the lever and mountings, 




Fig. 85. 

with the upper point, by the right-hand attachment bolt, 
and the other terminal connected with the lower point by 
the left-hand attachment bolt, which is insulated from 
the other parts. The movements of the lever can be 
adjusted by set-screws to any required range, as shown. 

When the key is not in use, the circuit is closed for the 
reception of a message from the opposite station by push- 
ing a short lever under a projection, as shown. But when 
a message is to be transmitted, the circuit is opened by 
moving this lever out of contact with this projection. 

The Sounder. — The receiving instrument most gen- 
erally used is called a sounder, the construction of which 
is shown in Fig. 85. A lever mounted on an arched sup- 
port, at the right, has a limited vertical movement between 



196 ELECTRICITY FOR EVERYBODY. 

the ends of a curved bar on the left, which can be adjusted 
to any required range by two set-screws. This lever has 
a short vertical arm, on the right, which is connected by 
a spiral spring with the post which supports the curved 
bar, as shown ; and the tension of this spring brings the 
lever into contact with the upper set-screw in the curved 
bar. An iron armature, attached to the center of the 
lever, is attracted downward by an electromagnet, in op- 
position to the force of the spring, when current is trans- 
mitted, bringing the lower set-screw into contact with the 
lower end of the curved bar. 

The magnet coils are connected with the electric circuit 
by the two binding-posts on the right ; and as current is 
alternately transmitted or stopped by the manipulation 
of the key at the distant station, the lever vibrates be- 
tween the ends of the curved bar, emitting a succession of 
distinct clicks, by which the message is indicated ; a loud 
click, when descending, and a fainter click, when ascend- 
ing, so that each kind can easily be distinguished. 

The Morse Alphabet. — The characters representing 
letters, numerals, and punctuation marks, invented by 
Morse for telegraphic communication, are given in Fig. 
86. They consist of four distinct elements, short dashes, 
long dashes, dots, and spaces, arranged in different ways. 
T, for instance, is represented by a short dash, L by a 
long one, E by a dot, I by two dots, by two dots sep- 
arated by a short space, J. by a dot followed by a short 
dash, W by a short dash followed by a dot, and so on. 

These characters were evidently employed on account 
of their special adaptation to the original method of re- 
ceiving the message, which was by marks made with a 
pencil or a steel point, on long strips of paper, fed auto- 
matically from a roller, in a machine called a register. 



THE TELEGRAPH AND TELEPHONE 



197 



But it was soon found that the message could be read 
much more rapidly by the clicking of the point than by 
the marks which it made; and hence the sounder, de- 
scribed above, was invented, and took the place of the 



A 



C 



D 



F 



H I 



J 



K 



M N O 



Q R S T U 



V 



W 



X 



Y 



& 



Period. 



Semicolon. 



Comma. 



Exclamation. 



Interrogation. 



Paragraph. 



Parenthesis. 



Fig. 86. 



register, though the register is still employed in special 
cases j a pen and ink being usually preferred to the em- 
bossing point. 

The clicks and pauses of the sounder have, in this way, 
come to represent the dots, dashes, and spaces of the 



198 ELECTRICITY FOR EVERYBODY. 

Morse alphabet. As the register point would evidently 
rest on the paper during the pause following a down 
click, making a dot, a short dash, or a long dash, accord- 
ing to the length of the pause ; or would be lifted off the 
paper for a corresponding time, during the pause follow- 
ing an up click ; so, in the sounder, a down click followed 
instantly by an up click, represents a dot ; a down click 
followed by a short pause, represents a short dash, or, fol- 
lowed by a long pause, a long dash ; an up click followed 
by a short pause represents a short space, or, followed by 
a long pause, a long space. The combination of sounds 
and pauses representing, in this way, each letter or charac- 
ter, is instantly recognized by the practised ear of the op- 
erator, who writes down the message with pen or pencil. 

In a modified form of this alphabet, known as the In- 
ternational, now used everywhere except in the United 
States and Canada, the space element, as in and other 
letters, is omitted, dots and dashes alone being used. 
This is the form used on all the cable lines. 

The Eelay. — When a telegraph line exceeds twenty or 
thirty miles in length, the loss of electric energy by the 
electric resistance of the circuit, and leakage from imper- 
fect insulation, render the current too weak to operate 
the sounder properly, and an auxiliary local battery is re- 
quired for this purpose, at each station, whose circuit is 
closed and opened by an instrument called a relay, which 
is so delicately adjusted that it can be operated by this 
weak line current. 

This instrument, shown in Fig. 87, is constructed with 
an electromagnet, which can be connected with the main 
circuit by the two binding-posts on the right. An arma- 
ture, supported on a hinge opposite the poles of this mag- 
net, carries a vertical lever, which has a limited vibration 



THE TELEGRAPH AND TELEPHONE. 199 

between two platinum points attached to set-screws, sup- 
ported on a curved yoke, as shown ; the left set-screw being 
insulated from this yoke. Two spiral springs, connected 
with this armature, a weak one below, and a stronger one 
above, operate against each other, and can be adjusted to 
any difference of tension required to make the vibrations 
of the lever respond promptly to the magnetic attraction 
of the armature 




Fig. 87. 

The circuit of the local battery includes the sounder, 
and is connected with the two binding-posts on the left, 
one of which is connected with the armature and attached 
lever, and the other with the curved yoke, through its 
support. 

When there is no current in the main circuit, the lever 
is pulled against the left insulated point by the upper 
spring, and hence the circuit of the local battery is open; 
but when current is transmitted through the main circuit, 
the armature is attracted and pulls the lever against the 
right point, closing the circuit of the local battery, and 
operating the sounder. 



200 ELECTRICITY FOR EVERYBODY. 

The vibrations of the lever can be adjusted to any re- 
quired range by the set-screws, and the tension of the 
springs being also properly adjusted, the instrument can 
be made to respond instantly to the weakest current 
transmitted through the main circuit; the sounder re- 
sponding simultaneously to the stronger current of the 
local battery, and to the manipulations of the operator's 
key, a hundred miles away. 

Cut-Out and Lightning Arrester. — Every telegraph 
station must be furnished with a lightning arrester, and 
also an apparatus by which the instruments can be either 
cut out of the circuit or connected with the earth, as may 
be required. 

The simple little apparatus shown in Fig. 88 fulfils 
these three functions. It is constructed with three brass 
plates, attached to an insulating base, with spaces be- 
tween them, so that they are insulated from each other; 
a brass plug being furnished by which they can be elec* 
trically connected. The two side plates are connected 
with the main circuit by the terminal wires attached to 
them above, and with the instruments by the wires at- 
tached to them below ; and the central plate is connected 
with the earth by the wire attached to it. Hence the line 
current, entering by either side plate, must traverse the 
instruments before it can leave by the other side plate, 
when all the holes are open, as shown. But if the plug, 
shown at the center, be inserted into the lower hole, the 
current will pass through it, direct from one plate to the 
other, without traversing the instruments. 

If, when the plug is out, lightning should strike the 
line wire, it will usually take the shorter route through 
the points, across to the central plate, and thence to the 
earth by the central wire, instead of the longer one 



THE TELEGRAPH AND TELEPHONE. 



201 



through the instruments. But as an unusually heavy 
discharge may divide, and part of it traverse and injure 
the instruments, it is important that they should be cut 




Fig. 88. 

out by the plug during a thunder-storm or the absence 
of the operator. 

If a break occurs in the line wire, by which the current 
flowing through a way station is interrupted, connection 
can be reestablished with the stations on the opposite side 
from the break by inserting the plug into the side hole 
next the break, so that current can flow through the 
instruments to the earth by the central plate and wire. 
If the break occurs on the left, and the plug should 
happen to be inserted first into the right-hand hole, the 
current would flow direct to the earth, without travers- 
ing the instruments 5 and the operator, perceiving this, 
would then move the plug to the left-hand hole, and 



202 ELECTEICITY FOR EVERYBODY. 

thus reestablish current through the instruments, and 
locate the direction of the break. 

Repeaters. — When messages are to be transmitted 
long distances, the battery current must be replenished 
before it becomes too weak to operate the relay. Hence 
main batteries must be located along the line wherever 
required for this purpose, by which current can be sup- 
plied for repeating the message from one of these stations 
to another, to any required distance. 

This requires the employment of two instruments 
called repeaters, at every such station, each connected 
with a main local battery, whose circuit can be closed 
automatically by the line current, which traverses both 
instruments, so that current can be transmitted from 
either battery according to the direction in which the 
message is to be repeated 5 the circuit of one battery 
being opened at the same instant that the circuit of the 
other one is closed. 

If, for instance, a message is to be transmitted from New 
York to Chicago, it must pass through several such sta- 
tions, at each of which the two repeaters may be distin- 
guished as the eastern and western. Current transmitted 
by the manipulation of the New York operator's key, 
automatically closes the local battery circuit through 
each western repeater and opens it through each eastern 
repeater, so that the message is repeated instantly, from 
east to west, all along the line. In like manner, when a 
message is to be transmitted from Chicago to New York, 
these conditions are reversed by the manipulation of the 
Chicago operator's key; each eastern repeater circuit 
being automatically closed, and each western repeater 
circuit opened. 

The repeater is simply a relay which operates a sounder 



THE TELEGRAPH AND TELEPHONE. 203 

by a small local battery, in the usual manner 5 and has 
attached to it an extra magnet, which opens and closes 
the circuit of one of the main local batteries for repeating, 
as above. 

Duplex Transmission.— The simple apparatus already 
described is sufficient for the moderate amount of busi- 
ness done on telegraph lines where the transmission of a 
message can be delayed while the line is occupied with 
the reception of a message ; but is quite inadequate for 
the transaction of the large volume of business done on 
many of the principal lines. Therefore, to prevent the 
expense and inconvenience of an excessive multiplication 
of wires, it became necessary to devise what is known as 
the duplex system, by which messages can be transmitted 
simultaneously, in opposite directions, by the same wire. 
This has been accomplished in two different ways, by 
means of relays of special construction, one of which, in- 
vented by Stearns, is known as the neutral relay, and the 
other, invented by Siemens, as the polarized relay. 

The Neutral Relay. — The neutral relay is con- 
structed with an electromagnet having two pairs of coils 
oppositely wound, one pair being connected with the line 
and the other pair with the earth, at each station. When 
an equal volume of current flows through each pair, the 
magnetic polarity is neutralized by the opposite winding, 
and no effect is produced on the armature; but when 
current flows through only one pair, or more current 
flows through one pair than through the other pair, the 
armature is attracted, closing the circuit through the 
sounder, and producing a down click. 

Transmission by the Neutral Relay. — Suppose two 
stations, A and B, equipped as shown in Fig. 89 ; each 
being furnished with a neutral relay, connected as above, 



204 ELECTEICITY FOR EVERYBODY. 

and also with a sounder and key, at each of which an 
operator is seated j and that messages are to be trans- 
mitted from each station to the opposite station, at the 
same time. The circuit being closed by depression of 
the key at A, current flows, in equal volume, through 
both branches of the relay ; one half going to the earth 
by the coils m and p, and the other half to the line, by 
the coils o and n, neutralizing the magnetism, and there- 
fore producing no attraction of the armature. But the 
half which goes to the line enters the relay at station 
Bj and traversing only the branch n' and o' connected 
with the line, produces attraction of the armature, and a 
down click in the connected sounder. 

If now the key at B is also depressed, current will flow 
to both branches of the relay, one half going to the line 
branch, o' and n', and neutralizing the line current from 
A, and the other half to the earth, through branch m' 
and p', so that the armature is still held attracted as be- 
fore. But the current through the line branch of the 
relay at A being neutralized also, while current still tra- 
verses the earth branch, the armature is attracted, and a 
down click produced in the connected sounder. 

Now if the key at A is opened, the current from JL's 
battery ceases entirely, so that current from B's battery 
flows equally through both branches of the relay at B, 
neutralizing the magnetism, and therefore releasing the 
armature and producing an up click in the connected 
sounder. But the current from B flowing in through 
the line branch of the relay at A, its armature is still 
held attracted as before. If now the key at B is also 
opened, B's battery current oeases entirely, releasing the 
armature at A, and producing an up click in the con- 
nected sounder. 



THE TELEGRAPH AND TELEPHONE. 



205 




206 ELECTRICITY FOR EVERYBODY. 

Hence it will be seen that each sounder responds to 
the manipulation of the key at the opposite station, as in 
single transmission, but is unaffected by the manipula- 
tion of the key at the home station ; so that there can be 
simultaneous transmission in opposite directions, by the 
same wire, without the slightest interference. Two of the 
three ground wires, at each station, traverse resistance 
coils, by which the resistance of this branch of the circuit 
is made equal to the line resistance, so that the currents 
traversing each branch of the relay shall be exactly equal. 
There is also a condenser connected with the ground wire 
of the relay, by which false currents, due to static charges 
of the line, are suppressed. 

Condenser. — The condenser is constructed with a 
number of sheets of tin-foil, insulated from each other by 
paper saturated with paraffin e. The ends of alternate 
sheets project beyond the paper and come into contact on 
opposite sides of the condenser j all the evenly numbered 
sheets being in contact on one side and all the oddly 
numbered sheets on the other side. Hence, when each 
side is connected with the electric circuit, as shown in 
Fig. 89, an electric charge, either positive or negative, 
produced on the tin-foil sheets on one side, produces, by 
induction, an equal charge of opposite kind on the other 
side, which can be employed as above, or in other ways 
equally important. 

Transmitter. — A transmitter, connected with the key 
and operated by a small battery, closes and opens the 
circuit through the main battery, and also through the 
central ground wire; always opening one circuit as it 
closes the other. 

The neutral relay, for duplex transmission, has been 
superseded by the polarized relay, which is a more sen- 



THE TELEGRAPH AND TELEPHONE. 



207 



sitive instrument; and it has been described only on 
account of its use in quadruplex transmission, to be 
described hereafter. 




Fig. 90. 



The Polarized Relay. — It is unnecessary to weary 
the reader with a full description of the polarized relay 
and its mode of operation. But it may be stated briefly 
that it is constructed with a curved steel magnet com- 
bined with an electromagnet, as shown in Fig. 90. The 
latter has two coils oppositely wound, as in the neutral 
relay, so that current transmitted equally through both, 
in a given direction, neutralizes the magnetism, but cur- 
rent transmitted through only one, or in larger volume 
through one than through the other, produces magnetic 
attraction of the armature. 

The armature is a small iron bar hinged to one pole of 
the curved steel magnet, so that it can vibrate between 



208 ELECTRICITY FOR EVERYBODY. 

the poles of the electromagnet, which is mounted on the 
other pole of the steel magnet, as shown. The two poles 
of the electromagnet are therefore permanently magnet- 
ized by the steel magnet, both having the same polarity ; 
and the armature, which vibrates between them, is also 
permanently magnetized, having opposite polarity, de- 
rived from the other pole of the steel magnet. The per- 
manent magnetism does not interfere with the temporary 
magnetism produced by the transmission of the current 
through the coils of the electromagnet ; but it makes this 
relay more sensitive than the neutral relay, so that it 
responds to weaker currents. 

The armature, having permanent polarity, is attracted 
by one pole of the electromagnet and repelled by the 
other, alternately in opposite directions, in response to the 
manipulation of the key at the opposite station j closing 
and opening the circuit and operating the sounder in the 
usual manner ; the connections through the relays at the 
opposite stations being such that simultaneous trans- 
mission, in opposite directions, is effected without inter- 
ference. 

A pole-changer is employed in connection with this 
relay, instead of a transmitter, as with the neutral relay, 
by which the direction of the battery current, through 
the relay, is changed from positive to negative, or the 
reverse, in response to the manipulation of the key. 

Quadruplex Transmission. — Simultaneous transmis- 
sion in opposite directions, by a single wire, having been 
accomplished, the next important step was simultaneous 
transmission in the same direction by a single wire. This 
was successfully accomplished by a combination of the 
neutral and polarized relays in such a manner that trans- 
mission could be effected through either instrument, by 



THE TELEGRAPH AND TELEPHONE. 209 

the other, without interference; the sensitiveness of the 
polarized relay having been increased and that of the 
neutral relay diminished, so that a battery current which 
would operate the polarized relay would not be strong 
enough to operate the neutral relay, while the stronger 
current required for the neutral relay would not interfere 
with the simultaneous operation of the polarized relay. 

Two opposite stations being equipped in this manner, 
it was found that, by a proper adjustment of the resis- 
tances and battery currents, four messages could be trans- 
mitted simultaneously, in opposite directions, by the same 
wire, two in each direction; and thus the problem of 
quadraplex transmission was successfully solved. 

This system has been in successful operation for many 
years on our principal telegraph lines ; but as it is very 
complicated, a detailed description would not be in accor- 
dance with the simple character of this book, and must 
therefore be omitted. 

Automatic Transmission. — Transmission by manipu- 
lation of the key does not exceed 25 to 50 words per 
minute ; a rate which is sufficient, in most cases, for the 
ordinary business of a telegraph office. But this mode of 
transmission is entirely inadequate for the large volume 
of telegraphic business done in large cities, including 
both press dispatches and private telegrams; especially 
on occasions of extraordinary public interest, or when 
accidental interruption of telegraphic communication has 
caused an accumulation of business. 

This led to the invention, by Wheatstone, of a system 
of automatic transmission, briefly described as follows : — 
The telegrams are prepared for transmission in an in- 
strument called a perforator, by which holes are punched 
in long strips of tough manilla paper, at the proper dis- 

14 



210 ELECTRICITY FOR EVERYBODY. 

tances to operate a transmitter in such a manner as to 
record the message in Morse characters, in a register at 
the distant station. 

A strip of paper, punched so as to record the word 
" toilet? would appear as in Fig. 91 ; in which is shown a 
row of small holes, at equal distances apart, between two 



o 




O 


O 


OO 


O 




O 


O 




o 


o 


o o o o 


o o o 


o o 


o o 


o o o 


o 


o 




O 


O 


O 


OO 




O 


O 




O 



Z o i leu 

Fig. 91. 

rows of larger holes, at different distances apart. A dot 
is made by arranging these holes as shown at e; sl short 
dash by the arrangement shown at t ; a long dash by the 
arrangement shown at I; and a space by the omission 
of the upper and lower holes, as shown in o, or between 
any two letters. 

When one of these strips of paper is placed in the 
transmitter, it is moved lengthwise at a uniform rate of 
speed, by a wheel underneath, having teeth adapted to the 
central row of holes. On each side of this wheel are little 
L-shaped levers, each having a short spur which is pressed 
upward against the paper by a spiral spring, so that 
when it meets a hole in one of the side rows, it passes up 
through it, and is pulled down again by a little walking 
beam; each lever operating alternately in this manner 
through the two rows of side holes. 

These levers are so connected with the battery circuit, 
as to reverse the direction of the current alternately by 
their upward movements ; one making it positive and the 
other negative, and thus operating the registering pen at 



THE TELEGRAPH AND TELEPHONE. 211 

the distant station • the positive current depressing it, so 
as to make a dot or a dash on a moving strip of paper, 
according to the length of time it is kept depressed, and 
the negative lifting it, so as to leave a space correspond- 
ing in length to the time it is kept lifted. 

Telegrams are transmitted automatically in this way, at 
the rate of 125 to 250 words a minute, about five times as 
fast as by manipulation of the key ; one operator feeding 
the strips into the transmitter as fast as a number of 
others can prepare them on the perforators ■ operators at 
the other end of the line transcribing the messages for 
delivery as fast as they are received. 

Submarine Transmission. — The telegraph cables which 
cross the ocean are composed of seven or more copper 
wires of medium size, twisted together and incased in a 
thick coating of insulating material, impervious to water, 
and covered outside with a protecting armor of zinc- 
coated iron wires,* this armor being much heavier near 
the shore, as a protection against ships' anchors, than in 
the deep sea. 

As the preservation of the cable from internal as well 
as external injury is of the highest importance, a com- 
paratively weak current is employed, which is never liable 
to heat the wires so as to injure the insulating material. 
The receiving instrument must therefore be so sensitive 
that it can be operated by this weak current; so that 
neither the sounder nor ordinary register, which require 
much stronger currents, can be employed. 

Reflecting Galvanometer. — The reflecting galvano- 
meter has the requisite sensitiveness, and was the instru- 
ment originally employed for this purpose. It is con- 
structed with a little concave mirror, about half the size 
of a dime, suspended vertically between two coils of fine, 



212 ELECTRICITY FOR EVERYBODY. 

insulated copper wire, by a silk thread attached to a brass 
ring above and below. A little magnetic needle is fast- 
ened to the back of this mirror, and when the cable cur- 
rent traverses the coils, this little needle turns the mirror 
to the right or left, according to the direction of the cur- 
rent, which is controlled by the key at the opposite end 
of the line. 

A ray of light, from a lamp, is reflected from this mir- 
ror, on a scale three feet distant, producing a round spot 
of light which rests on the zero mark, at the center of the 
scale, when there is no current traversing the coils, but is 
moved to the right or left, when the mirror is turned as 
above ; dots being indicated by movements in one direc- 
tion, and dashes by movements in the opposite direction, 
a slight turn of the mirror moving the spot several de- 
grees on the scale. 

This instrument is now but little used, the siphon re- 
corder having taken its place.. 

Siphon Recorder. — The siphon recorder, employed for 
the same purpose, is shown in Fig. 92. It is constructed 
with a small glass siphon, shown at A, lightly poised on a 
vertical steel wire axis inclosed in the tube B, the tension 
of which is regulated by an adjusting screw shown at the 
top of the tube. A short transverse spur from the upper 
end of the siphon is connected by a silk fiber, shown 
above the tube G, with one corner of a light rectangular 
coil of fine insulated copper wire, mounted on a vertical 
axis between the poles of a powerful steel magnet M. 
When this coil is traversed by the cable current, it turns 
in the magnetic field, to the right or left, according to the 
direction of the current, rotating the siphon slightly on 
its wire axis, against the torsion of the wire, and causing its 
point to oscillate across a strip of paper, which is moved 



THE TELEGRAPH AND TELEPHONE. 



213 



under it at a uniform rate of speed j being pulled to the 
left by clock-work, and unrolled from the wheel shown at 
the center of the magnet. 




Fig. 92. 



The point of the siphon, when at rest, is held exactly 
over the center of the paper strip ; being adjusted to that 
position by two soft iron armatures, which are slid to the 
right or left as required, on the poles of the magnet, and 
control two similar armatures attached to the vertical coil 
which moves the siphon. When the coil rotates in one 
direction, the strain of the silk fiber pulls the siphon point 
toward one edge of the paper, in opposition to the torsion 
of the wire axis, and when it rotates in the opposite direc- 
tion, the slack of the fiber allows the torsion of the wire 
to move the siphon point toward the opposite edge of the 
paper. 

This siphon is a capillary glass tube, the upper end of 
which dips into ink contained in a small reservoir, from 
which it is drawn by the siphon's capillary attraction, and 



214 ELECTEICITY FOR EVERYBODY. 

flows from its point in minute drops on the paper, pro- 
ducing a crooked line, as shown in Fig. 93, whose irregular 
curves and angles, projecting in opposite directions, indi- 
cate the Morse characters; dots being indicated by the 
projections in one direction, and dashes by the projections 
in the opposite direction. 

The point of the siphon has also a rapid vertical vibra- 
tion which causes the ink to flow, and prevents friction 
between the ink and paper, which would interfere with 
the horizontal movements by which the record is made. 
This vibration is produced by the electromagnetic ap- 
paratus shown under the glass shade on the right, which 
is operated by a local battery, and is connected by an 
electric circuit with the electromagnet shown under the 
point of the siphon at A. This apparatus consists of an 
electromagnet mounted on a vertical support, as shown, 
which operates a vertical steel spring vibrator by means 
of a soft iron armature attached to it above. This vibra- 
tor oscillates at the rate of about eighty times a second 
between two contact points, one of which is attached to 
the set-screw shown near its base, alternately opening and 
closing the circuit of the local battery ; the circuit being 
opened by the attraction of the armature, demagnetizing 
the electromagnet and allowing the vibrator to fly back 
and close the circuit, as in the operation of the vibrator 
of an electric bell, or an induction coil. 

A glass tube containing mercury is attached to this 
vibrator, as shown, and the hight of the mercury, which 
is adjusted by the tube and piston shown on the left, reg- 
ulates the rate of vibration ; this rate being diminished 
as the center of gravity in the mercury is raised, and in- 
creased as it is lowered; as in an inverted pendulum. 
The electric current passes through a resistance coil 



THE TELEGRAPH AND TELEPHONE. 215 

shown, having two circuits differentially wound, by which 
sparking at the contact points is suppressed. 

The electromagnet at A is included in the same circuit 
as this apparatus, and hence is also alternately magnetized 
and demagnetized by the oscillations of the vibrator ; and, 
when magnetized, it attracts a little armature consisting 
of a very small piece of fine iron wire, which is cemented 
to the point of the siphon, pulling down this point, and 
bringing the ink drop adhering to it into contact with 
the paper, the point being lifted again by the tension of 
the wire axis in the tube B, when the magnetic attraction 
ceases ; thus producing a vertical vibration of this point 
at the same rate as that of the spring vibrator, about 
eighty times a second, by which a dotted line is traced 
on the paper. 

The sole object of the various pieces of apparatus in 
this instrument is to produce simultaneously the two 
kinds of vibration of the siphon point; the vertical, by 
which the ink is drawn from the siphon, and the horizon- 
tal, by which the record is made. 

Automatic Transmitters. — Automatic transmitters 
are used, which are modified forms of the Wheatstone 
transmitter, already described. In one of these, invented 
by Wilmot, the perforated paper is used, and in the other, 
invented by Cuttriss, indentations in the paper are em- 
ployed instead of perforations. An average speed of 59 
words a minute is maintained with transmitters and re- 
ceivers of the latest construction, whereas 15 to 20 words 
a minute is the highest speed attainable by manipulation 
of the'key and the old receivers. 

Another very important advantage obtained by auto- 
matic transmission is uniformity in the shape of the let- 
ters, which makes the record much more legible, and 



216 



ELECTEICITY FOR EVERYBODY. 



reduces the liability to mistakes incident to manual trans- 
mission. Duplex transmission is also employed. 



A B 



E F G 

L & 




M 



H 



Q R S T 




U 



w 



n e 



dire 
Fig. 93. 



Cable Alphabet. — The alphabet employed is shown in 
Fig. 93, and also a sample of the record made on the 
paper strip, the letters in which can easily be recognized 
by comparing them with the alphabet. 

Static Charge. — The construction of the cable, with 
internal and external wires, separated by insulating ma- 
terial, makes it similar to that of a Leyden jar; so that 
when the current flows through the internal wires, a static 
charge is accumulated, as in the Leyden jar; the inside 
wires being oppositely charged from the outside wires 
and water in contact with them. This charge opposes 
and retards the current, so that a current wave sent 
through an Atlantic cable, by closing the circuit, does 



THE TELEGRAPH AND TELEPHONE. 217 

not attain sufficient strength for about three seconds to 
operate the most sensitive apparatus. 

Operation of Condenser. — The static charge makes 
it necessary to keep the cable constantly charged during 
transmission, so that the receiving instrument shall re- 
spond promptly to the flow of current, without waiting 
for the full rise or fall of each current wave. This is 
done by connecting the cable, through the receiving in- 
strument, with one pole of a large condenser, whose op- 
posite pole is connected with the earth ; and making such 
connection with the battery circuit, through the trans- 
mitter at the opposite end of the line, that the current 
shall be alternately reversed, through the condenser and 
receiving instrument, by the closing or opening of the 
circuit in the transmitter, but not interrupted. 

The condensers connected with the Atlantic cables, at 
each end, are composed of about 40,000 square feet of tin- 
foil. 

The Telautograph. — The telautograph, invented by 
Prof. Gray, is an apparatus by which a telegram can be 
reproduced at one end of the line in the same handwrit- 
ing in which it was written at the other end. This is ac- 
complished by two instruments, a transmitter, shown in 
Fig. 94, and a receiver, shown in Fig. 95. A pencil in 
the transmitter is attached by a pair of silk cords to 
apparatus connected with the electric circuit ; and as the 
message is written, this apparatus transmits electric cur- 
rents through the circuit, which reproduce identical 
movements in a pen attached to a pair of light aluminum 
arms, in the receiver, so that the message written in the 
receiver is a f ac-simile of that written in the transmitter. 

The receiving pen is a capillary glass tube, supported at 
an angle made by the junction of the arms, and supplied 



218 



ELECTRICITY FOR EVERYBODY. 



with ink through a small rubber tube attached to one of 
them. The paper in each instrument is supplied from 




Fig. 94. 

a continuous roll; and, in the transmitter, it is moved 
forward by the writer, as each line is finished, by a lever 




Fig. 95. 

shown on the left, which reproduces a similar movement, 
by electric transmission, in the paper of the receiver. 
The chief merit of this system of transmission consists 



THE TELEGRAPH AND TELEPHONE. 219 

in the fact, that the handwriting of the person sending a 
message can be recognized and identified by the person 
receiving it, and also that it dispenses with the service of 
the operator j so that important confidential business cor- 
respondence, or other correspondence of a strictly private 
character, can be carried on in this way, without risk of 
being counterfeited by designing parties, and without the 
publicity of ordinary telegraphic correspondence, which 
must pass through the hands of operators and clerks. 

Another important advantage is that diagrams and 
pictures can be reproduced, as well as handwriting j so 
that press correspondents can illustrate dispatches trans- 
mitted in this way. Messages can also be written in the 
receiver of a person temporarily absent, which will be 
found on his return. 

The Telephone. — The electric telephone is an appa- 
ratus by which articulate speech is reproduced at one end 
of an electric circuit, by electric impulses transmitted by 
the voice of a speaker at the other end. 

This apparatus is of an exceedingly simple character, 
and consisted originally of a single instrument, the well- 
known Bell receiver, which was employed at each end of 
the circuit, both as a transmitter and a receiver ; being 
held to the mouth for the former purpose, and to the ear 
for the latter. The electric current was generated in the 
instrument itself, without a battery, by the slight move- 
ments of an armature opposite one pole of a steel magnet, 
by the impulses of the voice. 

This system was improved by the addition of a trans- 
mitter of greater sensitiveness than the Bell instrument, 
which was still retained as a receiver, and also of a small 
battery to supply the current, consisting of a single sal- 
ammoniac cell. 



220 



ELECTRICITY FOR EVERYBODY. 



The Bell Receiver. — The Bell receiver, illustrated by 
Fig. 96, is constructed with a hard-rubber case about 6£ 
inches long, having an ear-piece at one 
end, with a hole in the center, opposite 
which is fixed the armature already 
referred to, which is a thin sheet-iron 
disk, about twice the size of a silver 
dollar, called the diaphragm, shown in 
cross-section by the line a a. Just back 
of the center of the diaphragm is shown 
the pole of a steel magnet, N 8, to which 
is attached an insulated coil of fine cop- 
per wire, c c, connected with the elec- 
tric circuit; and when a current is 
transmitted through the circuit and 
coil, the diaphragm, acting as an arma- 
ture, vibrates in response to the varia- 
tions of current strength, producing 
Fig. 96. air-waves, which reproduce the mes- 

sage spoken into the transmitter at the opposite end 
of the line. 

The diaphragm is held fast in the case by its rim, but 
it has sufficient flexibility to permit the slight vibrations 
required at the center; and enough space is allowed on 
each side of it, to prevent contact either with the magnet- 
pole or the mouth-piece ; the width of the space next the 
pole being so adjusted by the screw at S, as to produce 
the proper magnetic attraction. 

The Blake Transmitter. — The Blake transmitter, 
illustrated by Fig. 97, is the one usually employed on 
local circuits. The apparatus is contained in a wooden 
case, hung on the wall at the proper hight for speaking 
into, in the center of which is a funnel-shaped opening 




THE TELEGRAPH AND TELEPHONE. 



221 




employed for this purpose j opposite which is mounted a 

diaphragm a, like that in the Bell receiver. Just behind 

this is a little carbon disk, b, attached to a brass disk, 

suspended by a metal spring c, so that 

the carbon disk comes opposite the 

center of the diaphragm. The end of 

another spring, d, which comes between 

this disk and the diaphragm, carries two 

platinum points, one of which touches 

the center of the disk and the other 

the center of the diaphragm. These 

springs are attached to an iron arm, 

e, suspended by a spring, as shown j a 

short bevel on the bottom of this arm 

being in contact with an adjusting 

screw, by which the pressure of the 

platinum points on the diaphragm and 

carbon disk can be varied as required. 

The battery cell is contained in a separate compart- 
ment below, shown in Fig. 98, and its circuit passes through 
the springs c and d, and the disk b, and through a lever 
contained in a separate compartment above, by which the 
circuit is closed and opened. This lever terminates in a 
hook outside the case, in which the receiver is hung, as 
shown ; and the circuit is kept open by the weight of the 
receiver, which pulls down the lever ; but when the re- 
ceiver is taken off the hook, to be applied to the ear, the 
lever is pushed up by a spring, and closes the circuit ; so 
that current traverses the circuit constantly while the 
apparatus is in use. 

This circuit is connected with the primary circuit of 
an induction coil, also contained in the lower compart- 
ment ; and the secondary circuit of this coil is connected, 



Fig.97. 



222 



ELECTRICITY FOR EVERYBODY. 



through the main circuit, with the receiver at the other 
end of the line. 

When a person speaks into the transmitter, the pulsa- 
tions of the air, produced by the voice, produce the slight 
vibrations of the diaphragm, already referred to, and 
these vary the pressure of the platinum point on the 
carbon disk, and thus vary the strength of the electric 

current, and reproduce precise- 
ly similar vibrations in the dia- 
phragm of the receiver, at the 
opposite end of the line, which 
reproduce the spoken words. 

In the upper compartment of 
the case is a little magneto- 
electric machine, constructed on 
the same principle as the dyna- 
mo, and operated by the crank 
shown; and when a person, wish- 
ing to converse with another, 
turns the crank, an electric cur- 
rent is transmitted to the cen- 
tral station, by which an an- 
nunciator tablet, having this 
person's telephone number in- 
scribed on it, is exposed to 
view. The attendant then in- 
quires, through the telephone, 
the number of the person wanted, 
and being informed, rings a call 
on the bells in this person's telephone instrument, shown 
in Fig. 98; and the requisite connection being made be- 
tween the two, each converses with the other through a 
transmitter and obtains replies through a receiver held to 
the ear. 




Fig. 98. 



THE TELEGRAPH AND TELEPHONE. 223 

Difference Between Telephonic and Telegraphic 
Transmission. — It should be noticed that transmission 
by telephone is effected by varying the strength of a con- 
stant current in the electric circuit; so that the current 
rises and falls in waves, and thus reproduces not only the 
words spoken, but all the modulations and peculiarities 
of the speaker's voice, so that it can be recognized. 
Whereas ordinary telegraphic transmission is effected by 
closing and opening the circuit alternately, producing a 
series of brief currents, each of which begins and ends 
abruptly, and produces arbitrary sounds or marks. 

Construction of Telephone Circuit. — The construc- 
tion of the ordinary telephone circuit, employed for local 
transmission in towns and cities, is usually similar to 
that of a telegraph circuit ; a single line wire being em- 
ployed for one branch, and ground wires at each end, for 
the other branch; copper wire being used instead of iron, 
on account of its superior conductivity. But a complete 
metallic circuit, composed of two line wires, is also often 
employed, which gives more perfect transmission, but is, 
of course, more expensive. 

Each person employing the telephone requires connec- 
tion with a central station by a separate circuit. And, in 
a large city, there are several of these stations, connected 
together by as many main trunk lines as are required by 
the volume of business ; through which connections are 
made, in rotation, between persons connected with the 
different stations, in the same manner as between persons 
connected with the same station. 

Cross Talk. — The indistinct conversation, known as 
cross talk, heard through the telephone, by a person wait- 
ing, with the receiver to his ear, to be put in communica- 
tion with another, is due to electric induction between 



224 ELECTRICITY FOE EVERYBODY. 

numerous parallel wires mounted on the same brackets. 
This can be corrected on complete metallic circuits by 
crossing the wires, without contact, to opposite sides of 
the bracket, at regular intervals along the line, or twist- 
ing them together when in cables; an arrangement by 
which the induced currents on adjacent circuits, which 
always flow in the opposite direction to the inducing cur- 
rents, are made to oppose and neutralize each other. 

«— _s — * — ^ «— <— —* ^— * *— ^- — > 



_C 



XZ£ZX^)(ZD 



Fig. 99. 

The Long Distance Telephone. — This transposi- 
tion is adopted on all long distance lines, which are in- 
variably constructed with two wires. It is illustrated 
by Fig. 99, in which are shown two parallel circuits, 
mounted one above the other on the same poles, wire A 
over wire 0, and wire B over wire D, and each con- 
nected with a battery on the left. The arrows show the 
direction of the battery current in the upper circuit, and 
of the opposite currents induced by it in the lower circuit, 
which oppose and neutralize each other, as shown j the 
battery current in the lower circuit producing a similar 
inductive effect in the upper circuit, which it is not 
necessary to show. 

Long distance lines are constructed with much heavier 
wire than local lines, and are equipped with the solid 
bach transmitter, which has greater sensitiveness than the 
Blake transmitter, and is superseding it on local lines also. 



THE TELEGRAPH AND TELEPHONE. 



225 




Fig. 100. 



The Solid Back Transmitter. — The construction of 
this transmitter is shown in Fig. 100. It is made with a 
metal case having a fnnnel-shaped 
mouth-piece in front, which termin- 
ates in an opening opposite the cen- 
ter of a diaphragm a a, similar to 
that used in the Blake transmitter. 
Just back of the diaphragm is a lit- 
tle brass box, b b, lined inside with 
insulating material, mica in front 
and paper at the sides and rear, and 
filled with granulated carbon, in 
which are imbedded two little car- 
bon disks, c c and d d, each attached 
to a brass plate, one at the front 
and the other at the rear, supported opposite the center 
of the diaphragm. The front plate is attached to the 
diaphragm by a pin, and the rear plate is attached to an 
adjusting screw by which the pressure of the carbon disks 
on the granulated carbon between them is regulated. 

The disks being much smaller than the box, the carbon 
dust, which would be liable to accumulate between them 
and clog the granulated carbon, sifts down into the lower 
part of the box. The two plates are connected with op- 
posite terminals of the electric circuit, so that the cur- 
rent traverses the two carbon disks and the granulated 
carbon between them. The greater sensitiveness of this 
transmitter, as compared with the Blake transmitter, is 
due to the granulated carbon in contact with the carbon 
disks; carbon being superior to any other substance 
for this purpose, and granulated carbon superior to solid 
carbon. 

The speaker applies his mouth to the mouth-piece, in- 

15 



226 ELECTRICITY FOR EVERYBODY. 

stead of speaking at a little distance from it, as with the 
Blake transmitter. The Bell receiver is employed in con- 
nection with this instrument, in the usual manner, and 
also the call bell. 

The long distance telephone has been brought to such 
perfection by these methods, that two persons, 1,000 
miles apart, can converse through it as easily as if seated 
in the same room. 



CHAPTER X. 
The Rontgen X-Rays. 

Discovery of the Rays. — One of the most remarka- 
ble properties of electricity is the production, under cer- 
tain conditions, of rays which can penetrate bodies opaque 
to rays of light, and produce visible effects on specially 
prepared screens, and permanent pictures on photo- 
graphic plates and films. 

These rays were first discovered about 1891 by Hertz, 
a German professor, and subsequently investigated by 
Professor Lenard, of Bonn, and shown to possess the 
property of penetration to a very limited extent, being 
capable of passing through very thin sheets of metal 
and other substances. But their nature, source, and 
properties were very imperfectly understood by these 
investigators. This investigation was taken up by Pro- 
fessor Rontgen, of the University of Wiirzburg, who 
discovered that the rays could penetrate substances of 
considerable thickness, and produce the photographic 
and other effects referred to above. The visible effect on 
a screen was discovered accidentally November 8, 1895, 
and a full account of his discoveries was published about 
January 1, 1896. The term X-rays was chosen by him 
merely for its brevity, and without any special signifi- 
cance. 

Generating Apparatus. — To produce these rays, a 
Crookes vacuum tube similar to those described on page 

227 



228 



ELECTRICITY FOR EVERYBODY 



42 is employed, the construction of which is shown in 
Fig. 101. Two platinum wires, sealed into the glass in 
the usual manner, constitute the electrodes, by which a 

current of electricity 
may be transmitted 
through the tube. 
To the inner end of 
the wire on the right 
is attached a con- 
cave, aluminum disk, 
which is employed 
as the negative elec- 
trode, or cathode ; 
and to the inner end 
of the other wire 
is attached a small, 
flat, platinum disk, 
fixed at an angle of 45 degrees 
with the longer axis of the tube, 
as shown, and employed as the 
positive electrode, or anode; the 
relative positions of the two disks 
being such that rays collected by 
the cathode, acting as a concave 
reflector, are focused on the anode. 
The tube, or bulb, is exhausted 

to the usual high degree of vac- 
Fig. 101. . & 8 

uum mentioned on page 42; the 

best vacuum for this special purpose being carefully de- 
termined by experiment, and depending, to a certain 
extent, on the nature of the other generating apparatus 
employed. As the electric resistance of this high vacuum 
may exceed that of the glass, and the electric current, 





THE RONTGEN X-RAYS 229 

taking the path of least resistance, pass round through 
the glass, avoiding the inner terminals of the electrodes, 
the resistance of the platinum wires is made equal to that 
of the vacuum by extending them, as shown, in terminal 
tubes closed at both ends, which makes direct transmis- 
sion through the vacuum more certain. 

The tube is mounted on a stand by an adjustable 
clamp, to which it is attached by the terminal tubes, so that 
it can be set at any required angle, and is connected by 
its electrodes with the poles of an induction coil, capable 
of producing a spark four or more inches in length, and 
operated by a current from a battery or other generator. 
A primary battery of at least four strong, cells, like the 
Edison-Lalande, may be employed, or a direct dynamo 
current, but a storage battery current is usually pre- 
ferred. 

The current being transmitted from the anode to the 
cathode produces rays of light from each, the cathode 
rays being focused, as already stated, on the anode disk ; 
and here the X-rays, which are invisible, are generated, 
and projected at right angles to the axis of the tube, 
from the slanting disk, as a focal source, through the 
glass on any object placed within their influence. 

There is also a tube made with two platinum plates at 
the center, slanting in opposite directions, like the letter 
V, and two concave aluminum reflectors at the opposite 
ends. It was designed originally for use with the alter- 
nating current, the aluminum reflectors being made the 
electrodes, each acting alternately as anode or cathode 5 
the platinum plates being insulated, and the X-rays 
generated alternately on each of them as the polarity is 
reversed. 

This tube may also be used with the direct current by 



230 



ELECTRICITY FOR EVERYBODY 



making the platinum plates the anodes and the others 
the cathodes, dividing the current between them. A small 
tube connected with the main tube contains a chemical 
mixture from which, when the vacuum is too high for 
electric transmission, a gas is generated by heating with 
a lamp, which enters the main tube and reduces the 
vacuum. 

Induction coils have been fully described on pages 
108-12, and one with the spring vibrator shown there 




Fig. 102. 



may be employed for the X-rays ; but Fig. 102 shows a 
large Ruhmkorff coil designed especially for this purpose. 
Its primary coil is connected with a tinfoil condenser, 
placed in its base, as in all Ruhmkorff coils. At its side 
are shown two binding-posts, connected by set-screws 
with the terminals of the secondary coil, and having also 
set-screws for connecting it with the vacuum tube, and 
adjustable electrodes above, to show the spark-length. 
At the farther left-hand corner are shown two. binding- 
posts for connecting the primary coil with the battery 
and at the near corner a double-bladed reversing switch, 



THE EONTGEN X-RAYS 



231 



by which the direction of the current through the coil 
may be reversed when required. 

As there is always sparking at the contacts of a spring 
vibrator, or any current interrupter operating in the air, 




Fig. 103. 

which wastes the electric energy, a special interrupter is 
used in connection with this coil, the construction of 
which is shown in Figs. 103 and 104. 

It consists of a pair of wheels, placed one above the 
other and rotated horizontally in a tank of mineral oil, 
shown above, by a small electric motor, shown below, 
which is run by the current that operates the coil ; the 
upper wheel being notched. The terminals of the electric 



232 



ELECTRICITY FOE EVERYBODY 



circuit leading to the coil and tube are connected with 
two copper springs, acting as electric brushes, which 
press against the wheels, as shown in Fig. 103, the upper 
brush having a platinum tip, and the current is inter- 




Fig. 104. 

rupted at each revolution, as this brush breaks contact 
with the upper wheel at the notch. 

When the tank is elevated to its proper position, as 
shown in Fig. 104, this interruption takes place in the 
oil, which is a good insulator, and the contacts being im- 
mersed in the liquid, the spark is suppressed, and the full 
electric energy goes to the tube, less the small percentage 
required to operate the motor. 



THE RONTGEN X-RAYS 233 

As the electric strain on the insulation of a coil is very 
great, and liable to produce rupture, resulting in a short 
circuit within the coil, coils in constant use for this pur- 
pose are sometimes kept immersed in mineral oil, which 
greatly improves the ordinary insulation, especially at 
weak or defective points which may have escaped notice. 

The static induced current of an influence machine, 
described on page 35, may be employed in producing 
these rays, the electric energy being supplied by the 
machine, but the current from an induction coil is gen- 
erally preferred. 

Comparative Permeability of Different Substan- 
ces. — These rays are transmissible through all substances, 
solid, liquid, and gaseous, but with different degrees of 
facility, dependent mainly on the comparative density of 
the substance, and on its thickness; dense metals, like 
platinum, lead, and gold, tending to arrest and absorb 
them; while light metals, like aluminum and tin, transmit 
them j thin sheet aluminum being nearly transparent to 
them, while sheet platinum of the same thickness is 
nearly opaque, their absorption by the platinum disk of 
the tube making it red hot in a few seconds. 

In like manner, but in less degree, bone tends to arrest 
the rays, while the other animal tissues tend to transmit 
them. Glass, which is transparent to rays of light, is 
nearly opaque to the X-rays ; while wood, which is nearly 
opaque to light, is, to an equal degree, transparent to 
these rays ; and hard rubber, which is entirely opaque to 
light, even in thin sheets, is transparent to them in sheets 
of considerable thickness. 

Fluorescence. — Certain substances become fluorescent 
when exposed to these rays, emitting light visible in a 
dark room. This is true of glass, and also of various 



234 ELECTRICITY FOR EVERYBODY 

chemical salts and other substances, prominent among 
which are barium platinocyanide, calcium tungstate, cal- 
cium sulphide, rock-salt, Iceland spar, and uranium glass. 

Fluorescent Screen. — Apparatus constructed in ac- 
cordance with these principles is employed to produce 
visible effects with these rays. Rontgen employs for 
this purpose a paper screen coated on one side with bar- 
ium platinocyanide. Putting the tube in action in a dark 
room, and wrapping it in black paper, which completely 
confines the light produced within it, the screen, when 
brought into its vicinity, lights up with a brilliant fluor- 
escence which varies in proportion to the distance from 
the tube, remaining visible at a distance of more than 
six feet. 

If the hand be placed on the side of the screen next the 
tube, its shadow will be seen on the reverse side ; the flesh 
casting a faint shadow, and the bones a deep shadow, 
making a skeleton picture of startling vividness. 

The Fluoroscope. — Edison employs a similar screen, 
coated with calcium tungstate, which, he claims, has six 
times the fluorescent power of barium platinocyanide, 
and has constructed an instrument known as a fluoroscope, 
shown in Fig. 105, with a small screen of this kind, which 
has come into general use, and can be employed to pro- 
duce these X-ray shadows either in daylight or darkness. 

It is a box about seven inches long, made of stiff, black 
cardboard, with slanting sides, terminating, at the small 
end, which is open, in a cover designed to fit closely round 
the observer's eyes, and lined at the edges with some soft 
material, as plush or fur, to exclude the light. The broad 
end, which is about 7x9 inches in area, is coated on its 
inner surface with crystals of calcium tungstate, and con- 
stitutes the screen. 



THE RONTGEN X-RAYS 235 

This screen when exposed to the X-rays becomes fluor- 
escent, and the shadows of objects placed on its outer sur- 
face may be seen by an observer looking in at the small 
end, showing the peculiar effects hereafter described. 

The instrument is provided with a handle by which it 
can be held to the eyes, and is very convenient for vari- 
ous kinds of observations where a large screen is not 
required. 

Sciagraphs. — Pictures of these shadows can be pro- 
duced either on photographic glass plates or films, pre- 




Fig. 105. 

pared in the usual manner. Exposure of the plate or 
film to the light is not permissible for this purpose, as 
the picture would, in that case, be a true photograph of 
the object, produced by reflected light, and not of its 
shadow produced by the intercepted X-rays. Hence it is 
necessary that the plate should be inclosed, during the 
operation, in some substance opaque to light but trans- 
parent to these rays. This is done most conveniently by 
using as an inclosing envelop the cardboard case in 
which the plate is kept previous to its exposure, in which 
it is wrapped in two thicknesses of paper, one of which 
is black. 



236 ELECTRICITY FOR EVERYBODY 

The object being placed on this case, between the tube 
and the inclosed plate, the projected rays act on the sen- 
sitized plate through the envelop, but are absorbed by the 
different substances composing the object, in proportion 
mainly to their relative density and thickness, as already 
mentioned, leaving a permanent negative picture, having 
light shades where the rays are most absorbed, and dark 
shades where they are least absorbed. This negative be- 
ing developed by the usual photographic process, positive 
pictures are printed from it in which the lights and shades 
are reversed; giving true shadow pictures, in which the 
relative penetration of the rays is shown by the relative 
darkness of the shadows. 

The time of exposure varies from a few seconds to half 
an hour ; the tendency, as in ordinary photography, being 
to shorten the time as improved apparatus and methods 
are discovered. 

These pictures are known as sciagraphs, a name derived 
from two Greek words, scia, a shadow, and grapho, to 
write. They have also been called radiographs. It is 
evidently improper to call them photographs, as they are 
not produced by light, except as it is employed in print- 
ing from the negatives. 

Nature of the Rays. — The true nature of these rays 
is unknown, and no theory has yet been proposed in re- 
gard to it which is not more or less open to objection. In 
addition to their properties of invisibility, penetration, and 
chemical action, already described, they have another 
which distinguishes them from all other rays, either of 
light, heat, or electricity; they cannot be deflected from 
straight lines of radiation by any known means whatever, 
as other rays are deflected. 

Hence they can neither be refracted nor reflected, and 



THE RONTGEN X-RAYS 237 

therefore cannot be focused either by a lens or a mirror, 
nor made parallel. 

The cathode rays generated in a Crookes tube can be 
deflected from their conrse by a magnet, bnt magnetic 
influence produces no deflection of the X-rays 5 which 
seems to mark as a distinct property that which might 
otherwise be considered a result of their penetration of 
all substances. 

Light, according to a well-known theory, is produced 
by short waves, or undulations, of the ether, which are 
transverse to the direction of the ray, extending in all di- 
rections across its central axis like the radii of a circle. 
If a rav of lie-lit be transmitted through a crystal of tour- 
maline. it seems to become flattened by the molecular 
structure of the crystal, so that the undulations are all 
made to occur in a plane parallel with a line known as 
its optical axis. If another similar crystal be placed in a 
position parallel to this one, the ray which has passed 
through the first will pass through the second when the 
optical axes of both crystals are in the same plane, and 
produce a spot of light on a screen beyond. But if the 
second be given a quarter turn, so that the planes of the 
two axes cross, at right angles, the flattened ray can no 
longer pass through the second crystal, and the spot of 
light will be extinguished. If now the second crystal be 
given another quarter turn, bringing the optical axes 
again into the same plane, the ray of light will pass 
through as at first, and the spot of light be restored. 

This well-known experiment has long been accepted as 
proof of the transverse, undulatory theory of light, re- 
ferred to above, the flattening of the ray being known as 
its polarization. Applying this test to the X-rays, it is 
found that they cannot be polarized, but pass through 

16 



238 ELECTRICITY FOR EVERYBODY 

the crystals with the same facility when the axes are 
crossed as when they coincide in position. This, taken 
in connection with the fact that these rays cannot be de- 
flected, has given rise to the theory that they are produced 
by ether waves which undulate in the direction in which 
the ray is projected, and not transversely like the undu- 
lations in rays of light. 

Another theory is that the undulations are transverse, 
but much shorter than those which produce light, so that 
the ray can pass through the crystals without being pol- 
arized like the ray of light. Either of these theories,, 
more especially the former, will account for the penetra- 
tive power of these rays as compared with rays of light. 

Practical Uses of the Rays. —These rays are found 
to be an invaluable aid in surgery, showing the exact lo- 
cation of bullets, shot, and other foreign substances in 
the human body without resort to the painful, and often 
dangerous, operation of probing j and enabling the sur- 
geon to remove them with less cutting and risk. 

Internal malformations, cavities, and bony excrescences 
may also be shown in this way, and the extent and char- 
acter of fractures, dislocations, and decay of the bones ° r 
so that treatment can be given much more intelligently 
and expeditiously than formerly. In short, the surgeon 
and physician can now see inside the body, and are not 
limited, as formerly, to the formation of an opinion from 
external symptoms, often leading to wrong treatment and 
a fatal termination. Had this process been known when 
the lamented President Garfield was shot, the bullet could 
have been accurately located, and his life probably saved. 

Two views, obtained at different angles, may be re- 
quired to determine the exact location of the foreign 
substance, or the relative position of the parts in a frac- 
ture or dislocation. These views can usuallv be taken 



THE RONTGEN X-RAYS 239 

with, sufficient accuracy in a fluoroscope, and much more 
expeditiously than by a sciagraph, which requires time 
for the exposure and subsequent chemical development. 
As an illustration of this, a small revolver bullet was lo- 
cated so accurately by the fluoroscope that the surgeon's 
needle struck it at the first probing. Both methods have 
their relative value in different cases, the sciagraph being 
especially valuable where a permanent record is required. 

The employment of the X-rays in medical practice is, 
as yet, very limited as compared with their employment 
in surgery ; but, in G-ermany, physicians have succeeded, 
by means of them, in detecting and locating calcareous 
deposits in the valves of the heart and in other internal 
organs; so that they may yet become as valuable in medi- 
cine as in surgery. But they have not been employed as 
a remedial agency by any intelligent physician, and their 
reported germicidal qualities have been proved to have 
no foundation in fact ; experiments showing that the 
disease-producing germs, or bacilli, are not affected even 
when exposed to their direct action without the interven- 
tion of any protecting substance, much less destroyed by 
them when inclosed in the tissues of the body. It has 
been shown, however, that these rays can produce de- 
structive changes in those tissues ; effects similar to sun- 
burning, resulting in inflammation and blistering, having 
been caused by repeated exposures of the hand to their 
action. 

X-Ray Illustrations. — The following illustrations, 
taken from living subjects and material objects, will 
explain more fully the practical use of these rays in 
surgery and for other purposes. Each illustrates some 
special feature of X-ray work, similar illustrations of 
which might be multiplied to any extent, if space 
permitted. 



240 



ELECTKICITY FOR EVERYBODY 




Fig. 106. 

In Fig. 106 is shown the chest of a man who was shot, 
the bullet having entered at the front and lodged at the 
base of the fifth rib, near the spinal column. The time of 
exposure was fifteen minutes. As lead casts a darker 
shadow than either bone or flesh, on account of its greater 
density, it is easily located in all such cases. And as the 
shadow cast by clothing is very light, only the outer, 
heavy garments need be removed in taking such scia- 
graphs, the shadow of the lighter undergarments disap- 
pearing entirely in the picture. 

Fig. 107 shows a dislocated ankle, taken by an exposure 



THE RONTGEN X-RAYS 241 

of thirty minutes. The leg bone is shown projecting 
forward, at the joint, a considerable distance beyond its 
true place. In cases of this kind, views of opposite sides 




Fig. 107. 

of the dislocation may be required to insure sufficient 
accuracy. 



242 



ELECTRICITY FOR EVERYBODY 




Fig. 108. 



THE RONTGEN X-RAYS 243 




Fig. 109. 



244 ELECTRICITY FOR EVERYBODY 

In Fig. 108 is shown the arm of a man who was acci- 
dentally shot while hunting. The surgeon removed all 
the shot, as he supposed, and the wound healed; but 
subsequently a few more shot" were discovered, which, 
having become encysted, — that is, permanently inclosed in 
sacs, — were allowed to remain. Twenty-three years 
afterward, when the X-rays came into use, the man, wish- 
ing to know just how many shot were still in his arm, 
had this sciagraph taken, which shows thirty-four, in- 
stead of nine as was supposed. 

This shows the special value of the X-rays in such cases, 
as even the most skilful surgeon can never otherwise be 
sure that all the shot have been removed. Five minutes 
was the time of exposure in this case. 

Fig. 109 shows a fracture of the arm bone known as 
the radius, just below the wrist joint, on the right, which 
was taken by ten minutes' exposure. 

To an unskilled eye, a fracture is not very clearly de- 
fined in a sciagraph j but, in this case, a comparison of 
the bone at this point, with the same bone as shown in 
Fig. 108, reveals it distinctly. 

In Fig. 110 are shown sciagraphs of two cameos, cut 
on onyx, taken by an exposure of three minutes. This 
picture shows the beautiful effects of shading produced 
by the relative thickness of material, impossible to obtain 
in a photograph, which shows only the surface ; the figures 
cut in relief showing dark shades in the thicker parts r 
and shades of varying lightness in the thinner parts, 
especially those representing the faces and upper parts 
of the dresses; and all clearly defined above the light, 
almost transparent, background. Some of the finest and 
most delicate effects of the original sciagraph are' lost in 
the engraving. 



THE RONTGEN X-RAYS 245 




Fig. 110. 

It is an important feature of this process that not only 
prominent objects, as bnllets and shot, can be located by 
it, bnt also foreign substances so minute as to escape or- 
dinary observation. This is well illustrated by Fig. Ill, 
which shows a lady's hand, taken by fifteen seconds' ex- 
posure. 

A painful spot indicated the presence of some foreign 
substance which could not be found j but the sciagraph 
revealed a minute speck, just below the knuckle of the 
third finger, on the side next the little finger, as shown, 
which proved to be a little splinter of glass, the point of 
which was stuck in the bone. 

The delicate shading of this sciagraph is particularly 
noticeable, showing the folds of the flesh between the 
thumb and forefinger, and even the faint outlines of the 
nails, and the sharp bony prominences at their roots. 

Fig. 112 is a sciagraph of a man's hand, taken by an 
exposure of only three seconds, in which the difference in 
shading brings out all the parts prominently, notwithstand- 



246 ELECTRICITY FOR EVERYBODY. 




Fig. 111. 



THE RONTGEN X-RAYS 



247 




Fig. 112. 



248 ELECTRICITY FOR EVERYBODY 

ing the brevity of the exposure; the jewelled ring en- 
circling the finger, and standing out from the bone, is 
especially noticeable, the dense gold casting an intensely 
black shadow. 

Fig. 113, taken by three minutes' exposure, shows a 
block of Georgia pine, inch and a half thick, into which 




Fig. 113. 

six iron screws and two iron staples were driven. It is 
composed of two pieces, cut across the grain and glued 
together, the joint being shown in the center. The shad- 
ing shows with great distinctness the layers of the wood, 
their relative density, and the greater density of the 
iron. 

Fringes in the shadow are shown at the bottom and 
left-hand edges, while the upper and right-hand edges are 
sharply defined. This is due to the different angles in 
which the radiated rays impinge on the block, striking 
the lower and left edges at acute angles, and traversing 



THE RONTGEN X-RAYS 



249 



a comparatively small thickness of wood, and thus pro- 
ducing fringed shadows ; and striking the upper and 
right-hand edges, and especially the upper right-hand 
corner, at right angles, or nearly so, and hence traversing 
a greater thickness of wood, and producing a clearer, 
sharper impression, without fringes. 




Fig. 114. 

The greater thickness of air traversed by the oblique 
rays than by the direct rays tends to produce the same 
result ; the diffusion of the rays and their absorption by 
the air being directly proportional to the square of the 
distance between their source and the object on which 



250 ELECTEICITY FOE EVERYBODY 

they impinge. The difference in the clearness of in> 
pression of the different layers is dne to the same causes, 
and the darker shadows of the screws and staple on the 
right as compared with those on the left. 

Fig. 114 shows a picture of coins and a key, taken 
through a book of 656 pages, by an exposure of five and 
a half minutes ; the book having been laid on the case 
containing the sensitized plate, and the articles on its 
bottom cover inside, the rays being projected on it from 
above. 

In the center is shown an aluminum medal, and on the 
right of this a copper, five-centime, French coin, and 
above it a silver quarter dollar. On the left is shown a 
Chinese brass coin having a square hole in its center, and 
above this a nickel five-cent coin. Below the coins is 
shown a steel key, above which was placed a rubber band, 
quarter of an inch wide, which has nearly disappeared 
in the picture, showing that India rubber is practically 
transparent to these rays. The aluminum medal gives a 
faint shadow, showing its relative transparency as com- 
pared with the copper, brass, nickel, silver, and steel, all 
of which give dark shadows, showing little or no dif- 
ference. 

These rays may be employed to distinguish real gems, 
especially diamonds, from their cheap imitations ; the 
diamond being nearly transparent to the rays, while its 
imitation in glass is nearly opaque. 

This is well illustrated by Fig. 115, which represents a 
sciagraph taken with a small tube by an exposure of 
fifteen minutes. Real diamonds of various kinds cast the 
light shadows, numbered 13, 14, 15, and 16, while the im- 
itation, number 19, casts a dark shadow. It is also no- 
ticeable that the black diamond, number 20, which is a dull, 



THE KONTGEN X-RAYS 251 




Fig. 115. 



252 ELECTRICITY FOE EVERYBODY. 

lusterless substance, perfectly opaque to rays of light, is 
as transparent to the X-rays as the brilliants, while the 
diamond bortz, number 6, which is an imperfect brilliant, 
is much less transparent than either, but more so than 
the imitation, number 19. 

The garnets, 11 and 12, cast darker shadows than the 
imitation garnet, number 2 ; and the turquoise and pearl, 
4 and 5, much darker shadows than the opal 3, sapphire 
7, chrysolite 8, emerald 9, and ruby 10. The rough tour- 
maline, number 17, casts a darker shadow than the 
polished tourmaline, number 18, but this may be due 
merely to the difference in size. The darker shadow cast 
by the imitation amethyst, number 1, as compared with 
the imitation diamond, may also be due to the same 
cause, most of these imitations being made of glass, 
either solid, or pulverized and made into a paste; and 
glass, as we have seen, always casts a dark shadow. 



CHAPTER XI. 

WlEELESS TELEGKAPHY. 

Invention of the Wireless Telegraph. — In the 
latter part of 1896 announcement was made of the inven- 
tion of a new system of telegraphy, by a young Italian, 
Sig. Gulielmo Marconi, in which the transmission was 
accomplished through the ether of space, without the use 
of connecting wires or cables. Many experimenters before 
Marconi had been attempting to transmit messages with- 
out wires, and some had succeeded in a limited way over 
short distances. Marconi was, however, the first to pro- 
duce a system whereby wireless messages could be trans- 
mitted over considerable distances. As the elimination 
of wires and cables would mean a large saving in cost, 
and as there were also many places where neither wires 
nor cables could be maintained, but where it was desir- 
able to establish communication, this new method gave 
immediate promise of becoming an important commercial 
system. 

The Marconi Sending Apparatus. — The essential ele- 
ments of the early Marconi sending station are shown dia- 
grammatically in Fig. 116. In this diagram I is an ordi- 
nary induction coil with vibrator, the primary of which 
is connected in series with a battery and the telegraph key 
K. The secondary terminals of the induction coil are 
connected to two brass spheres mounted upon insulating 
stands and forming the spark gap S. One sphere is also 

17 253 



254 



ELECTRICITY FOR EVERYBODY. 



connected to the ground at G. The second sphere is also 
connected to a wire, A, which projects vertically into the 
air and is called the antenna. The operation of sending 



o s o 




K 



Fig. 116. 

is as follows : When the key K is pressed, the primary 
circuit of the induction coil is closed and sparks will 
jump across the spark gap between the two spheres. 
This will cause electric waves to be radiated out from the 
antenna into space in all directions, very much as light 
waves are radiated from a source of light. The higher 
this antenna, the greater the distance over which these 
waves will be propagated. These waves will continue to 



WIRELESS TELEGRAPHY. 255 

be sent out from the antenna so long as the key K is kept 
closed. If the key is closed for a short period, a short 
succession of electric waves will be sent out, while if the 
key is kept closed for a longer time a correspondingly 
longer succession of electric waves will be sent out. If 
the key is operated to send dots and dashes as in the ordi- 
nary Morse telegraph system corresponding short and 
long series of electric waves will be radiated into space. 

The Coherer. — At the receiving station means must 
be provided for detecting and indicating the presence of 
these electric waves. A sensitive detecting device was 
the principal element in the invention of the Marconi 
system of wireless telegraphy. The original form of this 
detecting device is the coherer. This consists of a glass 
tube about -§- inch in inside diameter, and two or three 
inches long, containing near the centre two short silver 
cylinders fitting tightly into the tube and separated from 
each other by about ■£$ inch. The space between the 
cylinders is about half filled with metallic filings, prefer- 
ably of nickel and silver. The tube may be left open, but 
for best results should be sealed and exhausted of air. In 
the latter case the two cylinders are connected to outside 
terminals by platinum wires passing through the glass. 

When these filings lie loosely between the metal cylin- 
ders, they offer a resistance of many thousand ohms to 
the passage of a current of electricity of low voltage, 
such as is obtained from a few cells of battery. If, how- 
ever, electric waves pass through the coherer, this resist- 
ance immediately falls to a few ohms, through which a 
current of electricity can pass readily. The filings will 
remain in this low resistance condition even after the 
electric waves cease to pass through them. If, however, 
the tube is tapped so as to shake the filings, they will 



256 ELECTRICITY FOR EVERYBODY. 

immediately return to their former state of high resist- 
ance. 

One explanation for this cohering action is, that the 
high resistance is due to contact resistance between the 
filings caused by thin films of vapor surrounding each 
filing, and that the electric waves cause minute sparks to 
leap across from filing to filing and thus break down this 
contact resistance by breaking through the thin films. 
When the filings are shaken they assume new points of 
contact, and the high resistance is, therefore, again estab- 
lished between them. 

The Marconi Receiving Apparatus. — The essential 
elements of the early Marconi wireless receiving station 
are shown diagrammatically in Fig. 117. In this diagram 
the coherer is shown at C, the two metallic cylinders 
being marked P. One of these cylinders is connected to 
the ground at G-, and the other is connected to an antenna 
similar to the antenna used at the sending station. The 
metal cylinders of the coherer are also connected to a 
local circuit containing a battery and a telegraph relay, 
R. In the secondary circuit of this relay is connected a 
battery, and a telegraph sounder, S, or a recording tele- 
graph instrument, and an electromagnetic vibrating de- 
vice, T, similar to an electric bell, called a tapper, which 
in its vibration strikes 'against the coherer tube. The 
operation of the receiving apparatus is as follows : 

The primary circuit of the relay R is ordinarily inter- 
rupted by the high resistance of the coherer filings. 
When electric waves strike the antenna, they pass down 
through the coherer to the ground, and in so doing break 
down the resistance of the coherer, thereby closing the 
circuit of the relay, which in turn closes the local circuit 
which operates the sounder S and the tapper T. As soon 



WIRELESS TELEGRAPHY. 



257 



as the tapper strikes the coherer the filings decohere, 
breaking the relay circuit and, therefore, also, the sounder 
circuit, and if the waves have ceased by this time, these 
circuits will remain open. If, however, the waves are 
still striking the antenna, all the circuits will again be 



[ 

T 



^ W^ 



H 



T 

i 



Fig. 117. 

closed. It is thus seen that so long as electric waves 
reach the antenna, the relay, sounder and tapper will 
vibrate continuously. If now dots and dashes are sent 
from the sending station, these will be received as short 
and long series of vibrations of the sounder. 
Self-Restoring Detectors. — A great drawback to 



258 ELECTRICITY FOR EVERYBODY. 

the use of the coherer with metal filings is the fact that 
the conductivity continues after the waves have ceased, 
so that a mechanical decoherer, such as a tapper, must be 
used to restore the coherer to its high resistance condition 
after each wave has passed. This not only involves 
mechanical difficulties, but also limits the speed with 
which signals can be received. 

To overcome this difficulty, a large number of self- 
restoring detecting devices has been developed. Some of 
these depend also upon contact resistance, but most of 
them depend upon the thermal, magnetic or electrolytic 
effects of the electric current. One of these is a self- 
restoring coherer, which has been successfully used in 
the Italian navy, and consists of a glass tube, similar to 
that used in a filings coherer, with two plugs of iron or 
carbon, placed a short space apart, and having a globule 
of mercury between them. Conduction through this co- 
herer exists only as long as the electric waves are passing 
through, and ceases the instant the waves cease. This co- 
herer is, therefore, self -restoring, and requires no tapper. 

A form of electrolytic detector which is very largely 
used at present consists of an extremely fine platinum 
wire, of which one end is made to barely touch the sur- 
face of a small quantity of dilute acid. This fine plati- 
num wire, measuring about .0001 inch in diameter, is made 
by casting a thin rod of silver with a platinum wire as a 
centre core, and then drawing this down to a wire a few 
thousands of an inch in diameter. The silver is now 
dissolved away at one end, leaving the platinum wire ex- 
posed. In this detector there is ordinarily contact be- 
tween the platinum wire and the dilute acid; when the 
electric waves pass through this contact is interrupted by 
the rapid evolution of gas produced. 



WIRELESS TELEGRAPHY. 259 

The Telephone as a Receiving Instrument. — The 
self -restoring detectors are often nsed with a telephone 
and a battery, in the local circuit shunting the detector, 
in place of the relay and sounder. This gives a far more 
sensitive arrangement, and can be used to detect much 
weaker waves than when telegraph instruments are used. 
The telephone is for this reason always used to receive 
messages transmitted over great distances. 

Interference of Messages. — The electric waves 
radiated out from the antenna of a sending station spread 
out in all directions, and every receiving station within 
their range would respond to the signals. For use on 
shipboard, or between ships and the shore, this is an im- 
portant advantage, because it enables any ship to com- 
municate with any other ship or with any shore station 
within the range of its wireless apparatus. Besides, 
where ships are scattered on the seas, the probabilities of 
interference are small. Where telephones are used to re- 
ceive the messages, it has, however, been found that a 
trained operator can select and read any one of several 
messages coming at the same time, because the signals 
from any one transmitter produce a characteristic tone in 
the telephone, due to the peculiarities of the particular 
transmitter. This is on the same principle by which it is 
possible to carry on a number of conversations between 
different persons in the same room. 

Tuned or Syntonic Signalling. — In order to avoid 
the interference of messages, methods have been devel- 
oped whereby a station can communicate with any one of 
several stations, without being affected by messages pass- 
ing from or to neighboring stations at the same time. 
This has been accomplished by tuning the oscillations of 
the sending and receiving stations, so that a receiving 



260 ELECTRICITY FOR EVERYBODY. 

station will respond to the signals from a sending station 
to which it has been tuned, but will not respond to 
signals from other stations. This is analogous to a 
tuning fork, which will respond to and be set into vibra- 
tion by sound waves of its own particular frequency, but 
will not respond to waves of any other frequency. This 
is done by combining with the sending and receiving ap- 
paratus, properly adjusted combinations of inductance 
and capacity, so that the sending station sends out waves 
of only one frequency, and the receiving station responds 
to waves of this frequency but is unaffected by waves of 
other frequencies. Sending apparatus which is not pro- 
vided with an adjusted combination of inductance and 
capacity, such as the simple apparatus shown in Fig. 116, 
will send out waves having a wide range of frequencies ; 
similarly receiving apparatus without this inductance and 
capacity will respond to any waves within a wide range 
of frequencies. Two or more stations which will send out 
and respond to waves of only one frequency, are said to 
be tuned to each other. 

Apparatus for Long Distance Transmission. — 
The distance over which wireless messages can be 
transmitted depends upon the strength of the electric 
waves radiated from the antenna, upon the height and 
construction of the antenna, and upon the sensitiveness 
of the receiving apparatus. Atmospheric conditions also 
affect the transmission. Under similar conditions, the 
signals transmitted between two stations are generally 
also much stronger at night than in daylight. 

For long distance transmission, the induction coil and 
battery are usually replaced by an alternating current 
dynamo and a high potential transformer, giving 25,000 
or more volts. Instead of a single wire, a combination 



WIRELESS TELEGRAPHY 261 

of wires is also used in multiple for the antenna to get 
the strongest effect. These have been variously arranged 
as elements of a cylinder, of an inverted cone, in the form 
of a fan, a grid, etc. In the transatlantic experiments 
made by Marconi, the antenna consisted of four high iron 
towers, with heavy wires stretched across their tops, and 
having a large number of wires radiating from these con- 
necting wires down to a common vertex on the roof of 
the station containing the wireless apparatus. 

Application of Wireless Telegraphy. — When Mar- 
coni's invention was first announced, many people pre- 
dicted that this new system would soon replace the wire 
and cable systems. Ten years have elapsed since this 
first announcement and the present time of writing, and 
the wireless system has become an established commer- 
cial business. It has not, however, displaced the older 
systems, but has rather found a field of application of its 
own. The large ships of commerce, as well as those of 
the important navies, have already been equipped with 
wireless apparatus, and a large number of shore stations 
have also been established, so that these ships now regu- 
larly communicate with each other and also with the 
shore. Many light-ships have also been placed in com- 
munication with the shore by wireless telegraphy, where 
previously a cable could only be maintained with great 
difficulty and uncertainty. The interior of snow-bound 
Alaska has also recently been placed in communication 
with the outer world by means of the wireless telegraph. 
Transatlantic wireless transmission has also been demon- 
strated as a possibility by the actual transmission of 
messages between England and America. 

While wireless telegraphy may thus be said to have 
passed the experimental stage, the army of investigators 



262 ELECTRICITY FOR EVERYBODY. 

who are studying the problems involved will doubtless 
accomplish much in the future to improve present 
methods. 



INDEX. 



INDEX. 



A 

PAGE 

Accumulator 79 

Accumulator, chloride, the 85 

Action, local 69 

Advantages of electric heating 185 

Agonic line 96 

Alphabet, cable 215 

" , Morse , 196 

Alternating current 107, 108 

" " dynamos 133 

" " " , exciter for 134 

" " motors 150 

Amalgamation of the zinc 68 

American storage battery cell 83 

Ammeter 18 

Ampere 18, 19 

Ampere's theory of magnetism 105 

Anion 92 

Anode 90 

Apparatus, generating 227 

Atkinson Topler-Holtz machine 28 

" " " four-plate machine 33 

Arc 168 

Arc lighting 165, 172 

Armature, dynamo 116 

" construction 125 

" , drum, cylinder, or Siemens' 126 

" , iron-clad, or Pacinotti 128, 134 

" , keeper or 98 

" , ring, or Gramme 126 

Arresters, lightning 161 

Attraction and repulsion, electric 20, 21 

" " " , magnetic 100 

Aurora 51 

" australis , 51 

" borealis 51 

" , cause of the 53 

" polaris 51 

Automatic telegraph transmission 209 

" " transmitters 210, 215 

265 



266 INDEX. 

B 

PAGE 

Batteries, electric 57-92 

" , storage 79 

Battery cell 57 

" " , Daniell 71 

" " , Disque Leclanche' 65 

" " , Edison-Lalande 69 

" " , Grenet 67 

" " , Law 61 

" " , prism, or pile, Leclanche" 65 

" " , Samson 63 

" " , Smee 60 

" cells, Bunsen and Grove 74 

" " , comparison between large and small 78 

" ,dry 70 

" " , gravity 72 

" " , Leclanche" 64 

" " , one-fluid 59 

" " , potassium bichromate 66- 

" " , two-fluid 59,70 

" " , voltaic 58 

" " , zinc-carbon 61 

" connection 74 

" " , parallel 76 

" " .series 75 

" , Leyden '. 25 

" poles 58 

" , primary 57 

" , secondary 79 

" , storage 79 

" , voltaic 57 

Bell telephone receiver 220 

Bells, electric 112 

Bipolar dynamo 130 

Blake telephone transmitter 220 

Break and make 110 

Brush discharge 36 

Brushes and commutator, construction of 129 

" for dynamos 115 

" " influence machines 29 

Bunsen and Grove battery cells 74 

Bus, neutral '. 179 

Bus-bars 177 

C 

Cable alphabet 215 

Calibrated 17 

Carpenter heater 185 

Carriers 29 

Cataphoresis 91 

Cathode 90 

Cation 92 

Cause of the aurora 63 

Cautery, electric 92 

Cell, battery 57 



INDEX. 267 

PAGE 

Chain lightning 47 

Charge, static, in ocean telegraph cable 216 

Chloride accumulator, the 85 

Circuit, closed 10, 66 

" , electric , 7 

" , magnetic 95 

" , open 10, 66 

" , short 108 

" , shunt 121 

Closed circuit 10, 66 

Coil, primary 108 

" , secondary 109 

Coils, induction 108 

Combs in static machines , 22, 23 

Commutator 116 

" segments 118 

Comparative permeability of different substances 233 

Comparison between large and small battery cells 78 

Compound wound dynamo 123 

Condenser 154, 206 

" , operation of 217 

Conducting electrode 58 

Conductivity 6 

Conductor, prime 22 

Conductors 6 

Connection, battery 74 

Consequent poles 99 

Conservation of energy 2 

Constant current and constant potential 124 

" " dynamo 125 

" potential dynamo 125 

Construction, armature 125 

" of armature brushes and commutator 129 

" " telephone circuit 223 

Controller 158 

Cooking, electric 186 

Core, magnet 103 

Counter electric pressure 141 

Crater in arc lamp carbon 168 

Crookes vacuum tubes 42 

Cross-talk telephone 223 

Current, alternating 107, 108 

" and circuit, electric 7 

" , direct 116 

" , electric 7 

" , faradic 112 

" , static induced 35 

" volume 8 

Cut-out in arc lamp 171 

" and lightning arrester 200 

D 

Daniell battery cell 71 

Declination of the magnetic needle 96 

Deflection of magnetic needle by electric current 100 

Dewey heater 182 



268 INDEX. 

PAGE 

Diaphragm, telephone 220 

Dielectrics 12 

Difference between telephonic and telegraphic transmission 223 

Dip or inclination of the magnetic needle 96 

Direct current 116 

" " dynamos 117 

Direction of rotation in influence machines 37 

Discharge, brush 36 

" , spark 32 

Discharger 26 

Discoveries, Tesla's 181 

Discovery of the X-rays 227 

Disque Leclanch6 cell 65 

Distribution, alternating current 181 

Distribution of power, electric 142 

Double carbon lamp 170 

" reduction motors 156 

Drum, cylinder, or Siemens' armature 126 

Dry cells 70 

Duplex telegraph transmission 203 

** transmitter 206 

Dynamo armature 116 

" , bipolar 130 

«* brushes 115 

" " , lead of 121 

" , compound wound 123 

" , constant current 125 

" , " potential 125 

" , evolution of the „ 114 

" , series wound 121 

" , shunt wound 121 

Dynamos 114-139, 116 

" , alternating current .- 133 

" and motors, relative size of 142 

" , direct current 117 

" , multipolar 131 

E 

Earth's magnetic poles 93 

" magnetism 95 

Edison-Lalande battery cell 69 

Edison storage cell 88 

Effect of breaking a magnet 99 

Electric retraction and repulsion 20, 21 

Electric batteries 57-92 

" bells 112 

" cautery 92 

" circuit 7 

" " , opening and closing 9 

" cooking 186 

" current 7 

" " and circuit 7 

" " , deflection of magnetic needle by 100 

" distribution of power . 142 

" " , natural 13 

" " , three- wire system of 180 

" energy 5 



INDEX. 269 

PAGE 

Electric generator, frictional >. 21 

" heating 182 

" " , advantages of 185 

•' induction 10 

«« ironing 189 

" lighting 165-181 

" lighting, arc 165 

u " , incandescent 172 

" motors 140-164 

" or magnetic storms 53 

" potential 7 

" power station, Niagara Falls 144 

" pressure 7 

" " and current volume, measurement of 15 

** " " rate of discharge in storage batteries 88 

" " , counter 141 

" railways 158 

"" resistance 6 

" " , heat and light by 165 

" transmission 6 

" " , loss of power in 146 

" " , nature of electricity and 1-19 

" units 18 

" welding '. 189 

" wind or souffle 42 

Electricity and electric transmission, nature of 1-19 

" generated by heat 191 

" , heat and 182-192 

" , magnetism generating 107 

" , nature of 1 

" , static 20-56 

Electrode, conducting 58 

" , generating 58 

Electrodes 58 

Electrolysis 89 

" in medical practice 91 

Electromagnetism 100 

Electromagnets 102 

Electrometer 35 

Electromotive force 7 

Electron 20 

Elementary principles of batteries 57 

" " " magnetism 93 

" " " static electricity 20 

Energy 2 

" , conservation of 2 

" , electric 5 

" , mass 3 

" , molecular 3 

Equator, magnetic 96 

Ether 4 

Evolution of the dynamo 114 

Exciter for alternating current dynamos 134 

F 

Faradic current 112 

Faure storage battery cell 81 

18 



270 . ► INDEX. 

PAGE 

Feeder wires 160 

Field, magnetic 15, 118 

Field-magnet 118 

Flaming 172 

Fluorescence 233 

Fluorescent screen 234 

Flnoroscope, the 234 

Force, electromotive 7 

" , portative 98 

Four-plate machine, Atkinson Topler-Holtz 33 

Frictional electric generator 21 

" " " , rubbers in 21 

Fuses 179 

G 

Galvanometer, reflecting 211 

Gearless motors 157 

Geissler vacuum tubes 42 

Generating apparatus 227 

" electrode 58 

Gravity battery cells , 72 

Grenet battery cell 67 

Grove battery cells, Bunsen and 74 

H 

Heat and electricity 182-192 

" " light by electric resistance 165 

" , electricity generated by 191 

" lightning 47 

Heater, Carpenter 185 

" , Dewey 182 

Heating, advantages of electric 185 

" , electric 182 

I 

Illustrations, X-ray 239 

Incandescent lamps 173 

Indicators, potential 18 

Induced current, static 35 

Induction coils 108 

" , electric 10 

" , magnetic 94, 95 

Inductors 29 

Influence machine, Atkinson Topler-Holtz 28 

" " , Wimshurst 38 

" machines 27 

" " , brushes for 29 

" " , uses of 41 

Insulation 6 

Insulators 6 

Intensity, magnetic 97 

Ironclad or Pacinotti armature ' 128, 134 

Ironing, electric 189 



INDEX. 271 

J 

PAGE 

Jar, Leyden 24 

K 

Keeper or armature 98 

Key, telegraph 194 

L 

Lamp, double carbon 170 

Law, Ohm's 9 

Law cell 61 

Lead of dynamo brushes 121 

Leclanche" battery cells 64 

Leyden battery 25 

" jar 24 

14 ", residual charge in 26 

Lighting, arc 105 

" , electric 165-181 

" , arc lamps 172 

Lightning 44 

" arrester, cut-out and 200 

" arresters 161 

" , chain 47 

" ,heat 47 

" , return stroke 46 

" , sheet 47 

Lightning-rods 49 

Line, agonic 96 

" , neutral 119 

Lines of force, magnetic 94 

Local action 69 

Lodestone 93 

Long distance telephone 224 

Loss of power in electric transmission 146 

M 

Machine, Atkinson Topler-Holtz 28 

" " " " four-plate 33 

" , Wimshurt 28 

Machines, influence 27 

Magnet core 103 

" , effect of breaking a — , 99 

" stone 93 

Magnetic attraction and repulsion 100 

" circuit 95 

" equator 96 

" field 15, 118 

" induction 94, 95 

" intensity 97 

" lines of force 94 

" needle, declination of the 96 

" " , dip, or inclination of the 96 

" shield 110 



272 INDEX. 

PAGE 

Magnetism 93-113 

, Ampere's theory of 105 

, earth's 95 

, elementary principles of . 93 

generating electricity 107 

residual 115 

Magnets, steel 97 

Make and break 110 

Mass energy 3 

Measurement of electric pressure and current volume 15 

Medical practice, electrolysis in 91 

Mercury vapor lamp 177 

Molecular energy 3 

" motion 5 

Morse alphabet 196 

Motion, molecular 5 

Motor construction, principles of 140 

Motors, alternating current 150 

" , double reduction 156 

" , electric 140-164 

" , gearless 157 

" , railway 155 

" , single phase 153 

" , " reduction 156 

" , stationary 147 

" , two phase 153 

Multipolar dynamos 131 

N 

Natural electric distribution 13 

Nature of electricity : l 

" " " and electric transmission 1-19 

" " the X-rays. 236 

Negative 7 

" battery pole 58 

Neutral bus 181 

" line 119 

" relay, telegraph 203 

" " , transmission by the 203 

Niagara Falls electric power station 144 

Nonconductors 6 



Ohm 19 

Ohm's law 9 

One-fluid battery cells 59 

Open circuit 10, 56 

Opening and closing electric circuit 9 

Operation of condenser 217 



Parallel connection of battery cells 76 

" system of electric distribution 178 

Pastilles 86 



INDEX. 273 

PAGE 

Perforator 209 

Permeability of different substances, comparative 233 

Plante" storage battery cell 80 

Plate, revolving, in Atkinson Topler-Holtz machine 28 

" .stationary" " " " " 28 

Polarity 93 

Polarization 59 

Polarized relay 203, 207 

Pole, negative battery 58 

Pole, positive battery 58 

Pole-changer 208 

Pole-pieces 15, 117 

Poles, battery 58 

" , consequent 99 

" , earth's magnetic 93 

Positive 7 

" battery pole 58 

Portative force 98 

Potassium bichromate battery cells 66 

Potential, constant current and constant 124 

" , electric 7 

" indicators 14 

Practical uses of the X-rays 238 

Pressure, counter electric 141 

" , electric 7 

" , coil 108 

Prime conductor 21 

Principles of batteries, elementary 57 

" " magnetism, elementary 93 

" " motor construction 140 

" " static electricity, elementary 20 

Prism, or pile, Leclanche" battery cell 65 

Push-button 10 

Q 

Quadruplex transmission 208 

R 

Railway motors 155 

Railways, electric 158 

Receiver, Bell telephone 220 

" , telautograph 217 

Recorder, siphon 212 

Recording watt-meter 162 

Reflecting galvanometer 211 

Register 197, 210 

Relative size of dynamos and motors 142 

Relay, telegraph 198 

" , neutral, telegraph 203 

" , polarized, telegraph 203, 207 

Repeaters, telegraph „ 202 

Report in electric discharge 37 

Residual charge in Leyden jar 26 

" magnetism 115 

Resistance, electric 6 



274 INDEX. 

PAGE 

Return stroke, lightning 46 

Reversal of rotation in motors 149 

Revolving plate in Atkinson Topler-Holtz machine 28 

Rheostats 147 

Ring or Gramme armature 129 

Rontgen X-rays, the 227-252 

Rotation in influence machines, direction of 37 

" " motors, reversal of 149 

Rubbers in frictional electric generator 21 

Running cars by storage batteries 161 



Samson battery cell 63 

Sciagraphs 235 

Screen, fluorescent 234 

Secondary battery 58, 79 

" coil 109 

Segments, commutator 118 

Self-induction Ill 

Series connection of battery cells 75 

" wound dynamo 121 

Sheet lightning 47 

Shield, magnetic 110 

Short circuit 108 

Shunt circuit 121 

" wound dynamo 121 

Simple telegraph equipment 193 

Single phase motors 153, 164 

" reduction motors . . 156 

Siphon recorder 212 

Smee battery cell 60 

Solenoids 104 

Solid back telephone transmitter 225 

Sounder, telegraph 195 

Spark discharge 32 

Static charge in ocean telegraph cable 216 

" electricity . . .20-56 

" induced current 35 

Stationary motors .' 147 

" plate in Atkinson Topler-Holtz machine 28 

Steel magnets 97 

Stone, magnet 93 

Storage battery 58, 79 

" " cell, American 83 

" " " , chloride accumulator, the 85 

" " " , Faure , 81 

" " " , Plante* 80 

" batteries 79 

" " , running cars by 161 

Storms, electric or magnetic 53 

Submarine telegraph transmission 211 

Switch 9 

T 

Telautograph 217 

" receiver. . . 217 



INDEX. 276 

PAGE 

Telautograph transmitter 217 

Telegraph and telephone 193-226 

" equipment, simple 193 

" key 194 

" relay 198 

" " , neutral 203 

" " , polarized 207 

" repeaters 202 

" sounder 195 

" transmission, automatic 209 

" " by neutral relay 303 

" " " polarized relay 208 

" " , duplex 203 

" " , quadruplex 208 

" " , submarine 211 

" transmitter, duplex 206 

M transmitters, automatic 210, 215 

Telephone 219 

" circuit, construction of 223 

" cross-talk 223 

" diaphragm 220 

" , long distance 224 

" receiver, Bell 220 

" transmitter, Blake 220 

" " , solid back 225 

Telephonic and telegraphic transmission, difference between 223 

Thermopile 191 

Three-wire system of electric distribution . 180 

Thunder 48 

Topler-Holtz machine, Atkinson 28 

" " " , " four-plate 33 

Transformers 236 

Transmission, electric 6 

TroUey 159 

Two-fluid battery cells 59, 70 

Two phase motors 153 

Tubes, Crookes vacuum 42 

" , Geissler vacuum 42 

" , vacuum 42 



Units, electric 18 

Uses of influence machines 41 



Vacuum tubes 42 

Vibrator 110 

Volt 17, 19 

Voltaic battery 57 

Voltmeter 15 

Volume of current 8 

W 

Watt 163 

Watt-hours 163 



276 



INDEX. 



PAGE 

Watt-meter, recording 162 

Welder 190 

Welding, electric 189 

Wimshurst machine 38 

Wind or souffle, electric 42 

Wires, feeder 160 

Wireless telegraphy 253-262 

" " , apparatus for long distance transmission 260 

" " , application of 261 

" " , interference of messages 259 

" " , invention of 253 

" " , Marconi receiving apparatus 256 

" " , Marconi sending apparatus 253 

" " , self -restoring detectors 257 

" " , the coherer 255 

" " , the telephone with 259 

" " , tuned or syntonic signalling 259 



X-ray illustrations 239 

X-rays, discovery of the 227 

" , nature of the 236 

" , practical uses of the 238 

" , the Rontgen 227-252 



Zinc, amalgamation of the 68 

Zinc-carbon battery cells 61 



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